boxers behavior

Question
I have a 4 yr. old boxer named Blinko. We recently bought a camp near a fishing lake. Blinko absolutely loves it. He is able to run free there. As for our home, we live in a subdivision. He runs free in a fenced in yard. A situation has recently occured with his behavior at the camp. When a stranger approaches by boat, he shows much authority, he is starting to growl  and bark at the strangers as if he is trying to protect us from any harm. It somewhat concerns me. I am confident he would never bite any of us or someone he tends to meet a bit. But i am leary about people he has never seen before. We cannot stop him from barking & growling, and people are becoming scared of him. He does not do this at home in our yard, only at the camp. I am trying to reassure people that he wouldn't bite, but i am not 100% on that one. any advice would be very helpful at this time.        thanks

Answer
Well what you can try is at first use a chock chain,pull him back and say 'NO! leave it!' and don't let people touch him,as that would be like praising for acting up,people can only touch him when he is not doing that-once he learns you will scould him and he won't get praise for it,he'll stop doing that

It might also help to talk to some trainers for some input as well,even putting him obedience classes might help