One of the ways I use to not have a one sided horse is to always change my diagonals with the terrain. This is easy to do in New England where our trails tend to not be long straight lines. I also change my diagonals on the straight tracks.
This does not mean my horse does not have a preference, he does and I get reminded of it when riding on the beach where there are no curves. But, he does not know about bumping the rider to the prefered side.
