Blimey, I dont profess to be any kind of designer!
But I do know plants, and awkward spaces! So I'll have a think...
How do you and the dogs feel about a 'maze' with bark or gravel paths, and local shrubs/trees, or fruit. It'll cut down the grass. And give them lost of twists and turns to race round and track.
It's actully quite simple to draw up your own plans. Start from a wall (house or boundary) and 'triangulate' the other edges from there. (use a compass and swing it both ways to make a crossover point at the correct distance - once you've worked out your scale)
Work out your permenent features (trees, manholes, pond etc) and add them after measuring distances.
Hang on, I'm being 'helped' by a German Shepherd.. I'll come back to this, cos Im sick of retyping where She's sat on the keyboard!