I really like Clinton Anderson's Lunging For Respect, parts 1 and 2, but if you get horrible winters and the footing is bad, then those are out of the question.
I do a ton of grooming and showmanship type stuff over winters, even in my barn aisle. Walk forward, stop with me on a loose or nonexistent lead, back up smoothly, again on a loose/no lead, turn on the forehand/haunches from each direction, set up, etc.
Parelli's 7 games can also be something to look into, to change things up, and perfect footing doesn't really appear to be imperative.
A stubborn horse walks behind you, an impatient one in front of you, but a noble companion walks beside you ~ Unknown