Harness

It depends on the individual rabbit. If the rabbit tolerates the harness well and does not freak out, then it is fine to use for short periods of time. However, it is extremely important to make sure the area in which you are using the harness is safe. This means no dogs, other animals, chemicals/fertilizers, or in the vicinity of a road. So a public park would not be a good place. The safest place to use a harness with a rabbit would be in your own fenced in backyard. If the rabbit happens to escape the harness, the fence should prevent him from running away.

I don't usually recommend a harness for rabbits. They can be just as dangerous for buns as they are for piggies. Have you checked out House Rabbit Society Rabbit Care Guide?