What are some good knots to tie a string bikini?

I have big boobs so I guess I'm an easy target for guys to pull at my strings and some girls at my school who are jealous also pull at my strings.

My mom has sewn the knots shut on the bottoms of my bikini. I double knot the strings on my bikini top, but once they find out it's double knotted they pull really hard.

Well............if you are really that provacative, I would wear a one piece swimsuit and get rid of the issue...........the men will like it just as much.