What do you do about a dog who is usually very sweet & affectionate, but is very aggressive when challenged. He has attacked other dogs without provocation. I tried to remove him from my car because of the heat. He refused & bit me severly.

From what I know Happy Tails is limited to cats.I would suggest calling a sanctuary that pertains to dogs. If you choose to seek the help of an Animal Shelter mention that he's not a family dog,he sounds as if he's had trauma- usually having the "challenged" part he might make a good roaming farm dog. You didn't mention breed - chows,Shepard's and pitbulls are challenging breeds,however it sounds like trust issues. If he's midsize you want to consider having more outings . I'm sorry he pushed back, not knowing why or speculating can be traumatic for both of you. If you are of loving and attached to him talk with an professional. Animals have different temperments just like us Sometimes it's a grumpy day. Good luck

It kinda sound's like he's starting to get very tatitorial, about certain areas. The only thing that I can suggest is to mix up some white vinegar, & water 50+50% put it in a spray bottle. Then whenever he acts aggressive, spray him with it all the while saying 'No', 'No.' Plus maybe try finding a trainer specialized in aggressive behavior. I believe that the ASPCA on Florin/Perkins Road offer's classes, but because of Covid-19 they might have modified them. You can Google them, & get much more information than I can offer.

How long has he been acting that way?