my garden is a bout 50ft long, and fully enclosed. I do let mine have the whole garden to run in, but only when I'm around - in case they find a way to escape or a cat gets in.
I do think that mine are at their happiest when they have the freedom of the garden they do amazingly high jumps as they binky about which they don't do in the run. Just have to keep them away from the veggie patch!