Guest dog paw/nail problem?

I would recommend taking him to the vet to make sure it isn't a vascular growth. It's not uncommon for dogs to develop growths on their paw pads. Many times they're just keratinous growths (kind of like corns) and can be clipped off with nail clippers (although these growths are more common in cats I have seen one or two on dogs). But without actually seeing the thing I would not advise taking the nail clippers to them yourself just in case they are vascular as they will bleed horribly if they are. Either way, it sounds like this dog needs his nails trimmed. Long nails are not only a cosmetic thing, they are also a potential hazard as they can get caught up on things and tear which is very painful. And in older dogs they interfere with how the weight is distributed on the feet which can exasperate arthritis.