" I can't seem to lunge my mare on a line without her pulling and falling out of the circle. When we are in the roundpen she does fine and out in a wide open space it's back to pulling...."
Sound familiar? It is a common issue. One that can a fairly easy fix, if you are consistent and willing to be patient. For the purposes of this question we are not discussing teaching a horse to lunge from the beginning, we are just going to discuss how to deal with a horse that has already developed this habit. Ok, I'm not being entirely honest, we ARE going to discuss how to start from the beginning since a fresh start is the best way to correct this issue long term.
The biggest mistake made when teaching the horse to lunge and while lunging in general is the thought process that lunging is to make our horse tired or to get rid of excess energy. This is the mindset that results in horses running full tilt circles in the round pen, making high speed pear shapes on the line and requiring a shank to keep from dragging their handling off to Timbuktu (note: I am not against the use of a shank or knotted nose band as a tool as will be explained in a moment). This mentality causes the handler to inadvertently chase their horse and with speed comes lack of balance on a circle, hence the pulling, falling out of the circle etc. especially (catch 22 alert) if the horse is not strong enough to hold the circle but needs to use the circle to become stronger and more supple.
So, what do we do then? FIRST THINGS FIRST! Reset your brain. Lunging, be it in the round pen or on the line, is not intended as a way to burn off energy like a child turned loose on the play ground, but a way to increase mental focus on the handler and increase strength, cardiovascular, and flexibility, think the same child in gym class learning to play a specific sport. Even a quick lunge before throwing a leg over is only intended to cement your horses focus so they are mentally prepared for the ride.
This is about to get very, very boring for some of you. Now, due to the specific circumstances of this question we are going to begin in the round pen, then build on each small victory and move out in to the big wide world.
A shank or a knotted nose band may be used here if your horse is tuning you out. HOWEVER do not nag, be very specific with your corrections. Quick and meaningful then beginning again. But please save this correction for last as we want to encourage our horse to relax and WANT to do as we ask, not be forced.
Beginning in the round pen, horse on the lunge begin with a small circle and ask your horse to WALK. Just walk. And after one half a circle ask for the halt, stand for 3 to 5 seconds (try to vary how long you ask your horse to wait so they do not begin to assume what you will want.) Ask your horse to walk on again BEFORE they become antsy and walk on their own. If you have a wiggler, as SOON as those feet stop moving PRAISE with a "good Whoa!" and again, ask for "walk on" before they think of it themselves. REPEAT. As your horse understands to whoa and wait, increase the time to wait but always mix it up between short and long waits. Sounds easy enough right? It is. BUT, you will likely have a horse that walks a few steps and tries to trot off, does the jig instead of walking. Decreasing the size of your circle can help reduce this. Remain calm. Ask for the walk, if you know your horse will only walk 5 steps before breaking in to a trot, walk them 3 steps and ask for the halt, repeat. Eventually you can get 5, 10, half the circle, and eventually the entire circle. Then of course the fun of changing directions and starting all over again ;).
So WHY am I telling you to just WALK your horse? The first think our horse needs to learn is to be relaxed on the lunge line and focus on you. That being on the line means it is time to work not time for a free for all. Doing this in a round pen (should you have access to one) helps reduce outside distractions and removes the temptation of "There is so much room I MUST FROLIC!" Obviously, this works outside a round pen as well, but may take a bit longer to obtain focus.
This part of the retraining will need to be repeated for several sessions. There will be nothing be walking on the lunge line until your horse can walk and halt both directions consistently. (I told you it is boring, but alas, a boring foundation is better than a dramatic trip to the hospital!)
Once your horse understands walking on the line we can add trot work. And yes, you are correct. You will be adding trot work the same as you began with the walk work. You will ask your horse to walk on and then as for the trot and after just a few strides your will ask for a downward transition back to the walk. It will be normal to have an excited horse that want's to rush, and this is why we are bringing them back down to the walk quickly, a reminder to still pay attention. Repeat these up and down transitions until you can allow a trot for a full circle and your horse quickly respond to the downward transition when asked (again, for a horse that wants to rush reducing the circle size helps with control). ALWAYS praise for the result you want, lavish the "good trot" when they are in a nice rhythm and paying attention, "good walk" when you get a nice downward or a nice walk, and "GOOD WHOA"! Again, the concentration of this exercise is for your horse to be focused more on you and waiting to receive a cue than being focused on running and playing. OF COURSE if your horse is hot and been standing they will be hard pressed to focus, but developing a routine of up and down transitions at "random" intervals will work their brain as well as their body. Soon you will be able to ask the same in the big wide world, and you will find that when you are away from home these exercises will be of comfort to your horse if they are nervous and help them settle in to work.
This process may take several days to several weeks to get your horse to where they are lunging softly on the line (even if they are quick and wound up they will still be focused) depending on your horse's disposition, prior experiences, and the quality of your communication. But it will work if you are consistent and clear with praise for each desired result. As your horse focuses on you, they will stop rushing, they will begin to hold themselves on the circle, strengthen and supple to where you can eventually ask for a canter with out them counter bending, leaning, and pulling.
Remember, there is no specific time frame your horse needs to learn this in. Do not rush through the steps because your pride stings or your find it boring. Not only will it help your horse over all mentally, but physically as well as lunging unbalanced can be the cause of many injuries and the early breaking down of joints.
The initial process may be frustrating, but remember, you and your horse are both relearning something you both thought you knew. Be patient and remember, all you have to do is not quit!