To be fair the mosaic in the OP is not connected to the epitaphs quoted. The mosaic functions basically like a sign on the gate announcing the place is guarded by watchdogs does today. Chaindogs mostly did not lead very enviable lives, and were probably not considered such a member of the family as the epitaphs convey.
It is an unfortunate fact that even though we have these rare pieces of evidence of human empathy and bonding with animals, the lot of the majority of animals falling into the hands of humans throughout history has not be very good.
Christian pop music is a pretty bizarre phenomenon, which apparently is pretty big in the US for obvious reasons.