So sorry for your loss, what a grand old age for a dog.
I must agree, I wouldn't trust any dog regardless of size or breed loose around the guinea pigs. Even if they mean well, they may accidently injure them trying to play with them. And at the end of the day, they are predators and guinea pigs are prey.
My piggy Dandelion is greatly interested in my dog and vice versa, but their relationship stays through-the-bars. Belgium and Dandelion run around together and interact, with Dandelion safely in his cage.
In any case, I would avoid dogs bred to hunt small animals such as rats. I wouldn't want a ratting dog even in the same house, just in case. (Same goes for ferrets.) Basically you don't want anyone that might be determined to crack open the cage in search of prey.