I thought that it had a problem with it's paw, but when my husband deals with him he is okay. Then this morning when I was just petting him on his back while my dog was 3 feet away drinking water, he growled and semi-attacked at me. This is a crazy dog and day one of a week stay! ??? I have never seen anything like this before and I have been with Rover for 2 years.
I have a "safety policy" with any pet that comes through my door. If a dog is presenting a threat to others or himself, he is removed from contact with whatever sets him off.
For this guy, I'd just give him his space. Stop trying to pet him, leave him alone on the couch with a blankie and a chew bone and let him do his thing. If it's time to go outside, just call him and coax him out.
I am so sorry you got bit and are having issues with this dog, its always very scary and can be quite painful.
First I would contact both Rover and the owner, let them know what happened, the owner might have insights as to how to deal with this and Rover should know about this so every body is aware and covered, plus they might have advice for you as well.
When we spend so much time around dogs, our own and others, we can easily forget that the dogs we sit are not ours and do not really know us at all, so we go about handling them the same we would our dogs and it can be a tad over whelming to them. Add the fact that they are in a strange place, with strange people, perhaps other dogs, so many things to adapt to all at once. Plus not all dogs like to be petted, this one is always a heart breaker when I have to explain it to clients who's dogs do not like physical contact but it does happen and this is a boundary that we need to respect for the good of the dog and the good of your relationship with him.
So I would approach this dog with this in mind, he is probably simply freaking out about everything, building his trust, letting him know he's got his space, always letting him know where you are in relation to him, never surprising him, that sort of thing will help so unless you have to handle him, just give him space, like the previous answer says, coax him rather than moving him, use food reward a whole lot, to get him to where you want to go, to when he's calm, etc. All these things will help tremendously.
But if you do not feel safe around him, if you fear for your family's or your dog's safety, I would see about finding him another sitter from Rover, perhaps somebody who is also a trainer (always look for positive reinforcement trainers) and let the client know you have an other option more suited for their dog.