How do I get my dog to stop nipping at me?

We got a 9y/o dachshund mix a year ago. He’s been amazing, except for one thing. On the couch or in med if you move your leg a little he’ll flip out and nip at it, specifically Your feet. It hurts, especially because I’m still healing from some breaks and it agitates my pain when he does it.

I know he has trauma from his previous owners. He’s scared on car rides in some areas, flinches at first when you go to pet him, was abandoned before we got him, at the foster home before we got him he was in a foster home with 8 other dogs at the same time because of an emergency placement (after he was abandoned he was found by a kill shelter and his original shelter had to get him fast). I think the nipping is a reaction from that.

We’ve tried telling him no and taking him off the couch, but it doesn’t work. Any advice? He’s my baby but the biting gets to be a lot. It used to only be an occasional thing but recently he’s been doing it a lot more.