Ground poles, like cavaletti, can assist in improving your pony's trot. Ground poles help your pony pick up his feet and have a nice elastic trot. They can also be used to encourage your pony to take longer or shorter trot strides. Moreover, they can be used when training any type of pony, and you can start using ground poles right away in your training. Introducing your pony to ground poles early on in his training will both make sure he is paying attention to where he places his feet and teach him to use higher strides. Both of these are lessons a pony should learn early on because they are critical to master for many ponyplay activities from pulling a cart to being in a show.
A ground pole is, like the name implies, simply a pole (usually wood or plastic) placed on the ground. Most often, there will be a series of ground poles spaced at strategic distances. The distance between poles will mostly depend on the gait they will be used at (i.e. will the pony be walking, trotting, or cantering over them). The pony will walk, trot, or canter over the poles while being driven or on the longe line. While you can certainly drive (or ride) your pony over ground poles, I think it is easier for a trainer to longe a pony over them, and so for this article I will assume you will be longeing your pony. However, the same principles apply to driving or longeing, and it is relatively easy to adapt longe line exercises to driving exercises.
Quite a few people use "ground poles" and "cavaletti" interchangeably. However, I will consider them as separate terms. When I say "cavaletti", I am specifically referring to poles raised off the ground, and when I say "ground poles", I am specifically referring to poles lying on the ground (not raised).
The first step is to setup some ground poles. You can either arrange them on a straight line, or on a circle. If you are longeing your pony, it might be easier to arrange them in a circle so you can remain at the center with your pony moving around you. However, you should try putting them in a straight line, and on a circle. Variation is great when training your pony. You should try to space the poles evenly at first. Once your pony has worked with ground poles a few times, you can start changing up the distances, but make sure they are spaced an appropriate number of strides apart for what you want to teach your pony and what gait your pony will be working at. The figure below shows a couple of possibilities for ground pole positioning when working on a circle. Alternatively, you can space them evenly in a straight line.
Now that you have your ground poles positioned just right, grab your pony (tack him up if you have not already done so) and walk him over to the poles. Lead him by the reins and walk him over each of the poles giving him time to step carefully over each one. Do this a couple times before you try longeing him over them. If you can, try trotting him in hand over the poles as well.
After manually walking (and possibly trotting) your pony over the poles, go ahead and hook him up to the longe line and send him out on a circle at a walk. Have your pony keep a consistent speed and impulsion over the poles. Carefully watch your pony on the circle: he should be keeping up a nice high stride both over the poles. Hopefully he will maintain this stride between the poles as well. Practice at the walk for a little bit, and definitely practice at the walk when you change up the number or spacing of the poles.
With your pony still on the circle, ask for a trot. Again, make sure that his speed is consistent throughout the circle. He may wish to slow down over the poles: you should not allow this. Whether you are working on a circle or a straight line, make sure that your pony is approaching each pole at a 90° angle. Obviously this will be more difficult the smaller a circle gets, but this is also a useful part of using ground poles (if you have a jumping pony, this will also prepare him for a jump course, where jumps should be approached straight on as well even though many jumps will be located right out of a turn).
Wait until your pony is comfortable trotting over the poles (this will take more than one training session) before you ask your pony to canter over them.
You can place the poles closer together to help your pony collect his trot, or space them further apart to assist in teaching extension. Try adding more poles or changing the geometry around. If you get to the point where your pony can work off line, try arranging the poles in a figure 8, or a serpentine. Once your pony is comfortable working over ground poles, there are endless possibilities open to you and your pony. The versatility and relatively low cost of ground poles makes them an ideal training tool to use in ponyplay. The greatest downside, in my opinion, is the space required to use ground poles. However, this can be said about many aspects of ponyplay. Even practicing gaits requires space. Of course, you don't have to use bio-equine sized poles; a shorter pole length (but similar diameter) could easily work in a backyard.
If you are able to train your pony over ground poles, try it and have fun!