making friends

Question
Kristin! Hi, i have had dogs all my life and presently own an adorable 5yr old male rottie. the problem im facing at the moment is with my neighbours st.bernard! he is quite aggressive towards me as i was away the first year of his life. now each time that i visit my neighbour, he has to be tied up and that is something i hate. initially when i did try to make friends, i asked her to let him lose while i sat quietly in a corner i almost got bitten! To be more precise, he sniffed me for a bit and then suddenly broke into aggression and went for my leg and got hold of my jeans and actually made a hole into it by the time he was pulled off. i still dont fear him as such but want to make friends at any cost. Also for your information, he is a perfectly friendly dog with family and ppl he knows from his early days. Please advise and oblige.
regards-Ardesh

Answer
He is probably over protective of his owners-what you can do is try to offer him some treats even without touching him but by tossing him treats,then slowly let him take them from your hand even if you do that for a while before eventually reaching out to touch him

also if he is not fixed that may make him more aggressive as well-and it might not hurt to mention that to his owners,as well