I got a request to do this by a friend, so i made a resource pack that replaces leads with collars, for all the good boys and girls out there.

It's marked as a 1.20.4 resource pack, but I believe it will work in any version 1.14+.

I'd like to note that this pack has very little function in-game. You have to force the lead into your armor slot with commands for you to wear it.

To wear it without commands, either you need a mod to put it there, or a server you're in should have a hat plugin to apply an item to your head.