I stopped using any kind of collar on Pico when I heard about how soft their tracheas are and how easily than can be collapsed. He, too, is a nudist and I only put the harness on when I put him in his car seat. I clip it to the strap on the seat belt so he won't fly around if I stop suddenly or get into an accident.
I use it when I am putzing around outside and want him to enjoy the yard and put a 30 foot soft lead on the harness. He seems to feel very inhibited with that lead on it even though it is not tied off to anything and he doesn't wander the way he does without the lead dragging behind him. If he does get too close to the curb or starts to wander off or even run, in just a couple of steps I can step on the loose end of the lead and stop him, then pick it up and coax him back into my area again.
Tugging on the harness only puts pressure on the chest area whereas the collar puts pressure on the trachea. I worry enough about him without adding to the risks with a collar :wacko: