Charlie is our new puppy Cavalier King Charles Spaniel. She has taken great interest in the guinea pigs and seemed to want to play with them -- but we were not taking any chances. The GPs are very well protected in a cage. Only either Charlie can be out of the cage or the GPs, never both together. Charlie pounces and grabs things that move and shakes them vigorously. We do not trust her with our precious GPs.
Fluffy and Charlie seems to like each other very much. Fluffy comes to the side of the cage and popcorned when he sees Charlie and Charlie likes to "sniff" Fluffy's nose through the cage while doing a puppy bow (meaning she wants to play). It's quite a sight. But yes, Fluffy also pounces on the cage (trying to startle the pigs and make them run).