Poor Boomer!

Three of ours don't mind the harness because they associate it with going out and having fun. Pickles, well, he is his own cat and refuses to have anything adorning him ... it made me sad to see him hide under the bed with his harness so we don't bother him with it now.

Can you re-start training Boomer with a collar, because it shouldn't be as intimidating as a harness? Then, slowly re-introduce the harness to him. Good luck.