I had 3 guinea pigs and now I have a rabbit. Both these animals often damage their legs.

If it happened, first of all you must recognize what was damaged. If your pet has blood on its legs or it licks them your rabbit or guinea pig pulled out its nail. Take your pet and find out if the nail was pulled out completely or broken. If it is broken you should remove the broken part with scissors - it will be better if you have special scissors for rabbits (they're good for guinea pigs and cats too). Be careful! Rabbits and pigs have veins inside their nails! Never cut off too much!