I used revolution for my rats, and I lightly wetted and parted their fur between their shoulderblades so I could get direct contact to the skin easier, and so they can't reach it quite as easily. It's supposedly pretty safe to use, so 2 drops directly onto the skin should be totally fine, it's what I used for my rats (ranging from 250g-almost 1lb) and that fixed everyone right up very quickly! I also treated my hairless girl just to be safe. Just make sure it dries before letting them go. Good luck!