My sister keeps her miniature Palomino mare in my back yard (3/4 of an acre). I exercise her just by sending her away from me (as in join-up) for about 10 to 15 minutes. She then wants to come to me and she's had a good workout. We are thinking of putting her into work with a cart...and ground driving her too.
Another horse owner in the area has a mini that had previously foundered regularly and she walks him like a dog. It's a strange sight but everyone knows both her and her pony!