Keeping the guinea pig safely in its cage will ensure its safety. Keep the cage in your room and keep the door closed. That way, there is no chance that the kitties will get it.

First of all you need 2 guinea pigs as they rely on each other for company and body warmth. Also if the guineas are in the cage long enough for the cats to get used to them then there shouldn't be a problem when they all start roaming around together. When I was a child I bred Guineas,heaps of them, and there was never a problem with our cat bothering them. When they are out of the cage and roaming around the yard keep a very close eye on them because the neighbouring cats and dogs will jump in like a flash and have them.