I don't have the time to read all the replies on here, so incase this has already been said excuse me.
Did you pick your cat up and bring him outside?
I've found a better way, so that the cat adjust on his own time, and there's is less chance if him freaking out. Is to just open the door... and stand there with him (not in your arms) while he's wearing a harness. Be it a couple seconds or a half an hour, your cat will probably move on his own time and creep outdoors.
It's a very slow process, it's not like walking a dog.
What did you do when he tried to escape? Did you walk with him, so that he couldn't slip the harness, did you stand still, or did you pull on the leash to try and get him to come to you?
Did you pick your cat up and bring him outside?
I've found a better way, so that the cat adjust on his own time, and there's is less chance if him freaking out. Is to just open the door... and stand there with him (not in your arms) while he's wearing a harness. Be it a couple seconds or a half an hour, your cat will probably move on his own time and creep outdoors.
It's a very slow process, it's not like walking a dog.
What did you do when he tried to escape? Did you walk with him, so that he couldn't slip the harness, did you stand still, or did you pull on the leash to try and get him to come to you?