I put the harness on my bunny and put them in thier hutch, let them get used to it (make sure you keep an eye on them!) did that for a few days, then added the leash, and i walked with them in the garden, did that for a while. I also take them to quiet paths nearby. make sure you always protect them from dogs when you are out. You can take them out and give them thier favourite treats, to associate it with a good thing. but if they still dont like it, as Korr and Sophie said, dont keep using the lead if they get stressed. good luck!