I had/have the same problem w the prong and my boy. I ended up using another collar to sorta hold the prong up. I don’t know if that makes any sense. His regular collar is just to have his name tag & license on him so it sits low. When we go for our walks I put his prong on then another collar w a snug fit (but not too tight that it’s uncomfortable or restricting for him) & use a carabiner to attach the 2.

It’s not fool proof though. During our walks if he walks in heel then we’re usually fine. It’s when I let him walk freely ahead of me that the prong tends to slide down. I just take that opportunity to practice commands like stop & sit to readjust the prong back up. It’s not too bad and it’s been the only solution I could come up with for the issue. Thanks for posting the question, I hope someone else has a better solution for both of us!