Flee collars for rabbits?

I just built a huge cage and run for my rabbits in the backyard. I live in the country so there is probably a lot of fleas, ticks and small insects. I would like to put cat flee collars on my rabbits to be sure they will still be healthy and eliminate the chance of them getting fleas. Would this be okay? The part that concerns me is that the medication may be to much for their body weight. I have 1 medium(4-5 lbs) sized rabbit and 2 (2-3 lbs) small ones.