Surfing Waves

I finally gave in and bought 2 stickers for my foamie. After a couple of days, 1 of them had come off while the other one is sticking strong and shows no signs of coming off. Why is that? Is there such a thing as "waterproof stickers"? If so, where could I get them?

I dont know anything about this kind of stuff, so if anyone has had experience with it, I'd appreciate it. Thanks