I have no idea what my dogs breed is

I found my puppy about a month ago outside in Austin and when I got him he was very underweight, full of worms, and dirty. Every vet has asked if he’s pure bred and I can not figure out what he is! His paws are huge, his fur is not soft at all (it’s very think and coarse), and he’s about three months and 14 pounds now. he’s definitely a mutt but any guesses?