Well you may not like this advice but I have worked with children of potty training age for several years...the one thing I have found that does help is to not make is so easy for him. When he does have an accident, have him help you change his soiled clothes. The more he can do the more effective. I am not suggesting in any way that this be a punishment or anything of the sort...it is just what happens when we have accidents...pee pee or poo. I stayed encouraging and positive but just explained.."I need your help with this...please take off your pants and put them in the bag (washer, etc.)" Have him use wipes to clean himself...and so on.
It is SO common for kids to do this so take it easy on yourself. Also realize that learning to pee is a different sensation than learning to poo. It is essentially like learning two different skills not one. It will come but let him be an active learner instead of you doing all the dirty work. Of course lots of handwashing and sanitizing will need to take place.
Other things to consider:
Does he go at the same time everyday? IF so, have him sit and try about that time. Set a timer if need be to keep him on the potty longer..."oh, sorry honey, the timer is not finished yet"
Maybe plan a favorite activity for just after he goes..."we can't go outside until you go potty"
Avoid power struggles...this is one of the last major things a child has control over, so if it turns into a struggle...game over.
Good luck, and hang in there.