How do you deal with neighbors that never mind their own business?

Ever since we moved here the neighbors seem nosey .They sent us letters asking us if we ever walk our dogs because they are in a kennel and we had only been here for three months and since then we had a privacy fence put up so we can let them run the yard. I never seen them walk their dogs since we been here .The neighbor guy is always on his porch watching me as I pull up and I caught him in our yard a few times.He has an old lady and three kids that never leave the yard or house and It seems that they always have too much time on their hands.