I don't even think I would get a harness on any of mine! Tried putting a harness on Cheese before but she wasn't having any of it - took about 2 hours.
Put a harness on one of my ferrets years ago, Snowball.
You would have thought it was the most heavy thing she'd ever had on her the way she collapsed onto her back with a paw in the air.
Soon as I took it off she got up and walked away like nothing happended, she was such a drama queen.
Lirael can wear them until she realises the leash is there as part of it and then attacks it.