My horse and I have the attention spans of gnats, so here's another one. Four poles placed in a square, making a 9' box. For warmup, trot in and out, canter in and out, figure 8's to change direction, whatever floats your boat. To ramp up the level of difficulty, transition from trot to canter or canter to trot while inside the box. Gives you one shot to time it perfectly. If you're feeling really good about your riding, halt your horse inside the box at all 3 gaits.
You just have to see your distance...you don't have to like it.