Runaway Lab!

I cannot seem to keep my yellow lab home and within his fence for anything! I had him neutered thinking this may solve the problem,it has improved some,but the minute you take your eye off him he's under the fence. He was 1 1/2 yrs old when he was nuetered,so I'm thinking he got a taste of something he likes and has yet to forget! Around 1 yrs old was when I adopted him and I think he may have been abused by children? Many a kid he does not like!! He seems to have an agressive side to people he does not know/like? Anyone associated w/ me he seems to be fine with (sometimes!). Any info would be helpful,I'm running out of ideas.