Ok, I'm going there. When our kids started squirming away from diaper changes, a "no" with a good sting to the butt nipped it in one try. Not angry, just teaching, like a momma lion nips a cub, that's not what you do during a diaper change. After that, all we needed was "no" a couple of times, and after that, it was just a given that you're still during a change.
At 17 months, he's sort of strong willed and it may take a few more tries. We did it younger. Despite the unfathomable abusive cruelty some will claim that is, the kids were content thereafter to cooperate which made everyone happier. Sometimes kids learn they want to squirm, kick, scream, whatever during diaper changes. They're just trying, and don't know better. You can manage it with tag team diaper changes to a fighting child, or nip it. Your choice! Whatever you do, don't say "no" without enforcement, because that just teaches that "no" means nothing, so they'll never head it as a request the next time around.
With our first, we were reluctant because it was our first discipline EVER as new parents, and even though all our relatives did it, and told us it would work, I wasn't ready, and let it continue with wrestling. Until one day the little squirmer's foot caught a full loaded diaper in the back of our car during a road trip flinging poo everywhere that we had to smell for days in a heat wave.....we decided it was time. The next two babies learned on the very first try.