I usually keep it light during the winter months as well due to bad weather. To keep them legged up I go back to perfecting the basics, focusing on getting them really keyed in to working off my seat and leg cues to keep them light and responsive (especially after a long, hectic season on the road). Roll backs, figure eights, side passing, stopping and backing. I even throw in some training from other events to keep their minds fresh like teaching them how to pull barrels or small logs around, trotting poles, and even some western dressage moves. Another good one is teaching your horse to back perfectly in a box/square pattern and a round pattern. You would be amazed how many muscles they use and how it keeps their minds sharp.