Most people underestimate the power of a few million circles at a lope. It will slow a horse down, level them out, and teach them cadence. I personally prefer doing my circles in a larger area like a large arena or pasture where the horse has to follow your cues instead of just following the fence. Teaching a horse to circle under saddle doesn't happen overnight and it will take time and patience on the riders side. The circles will be uneven and there are certain sides that they will be faster or slower on. Just keep at it and it will help with almost anything.