Have you ever had a dog suddenly start peeing in his own bed? Is it a territory thing? I guess I've had some dog visitors lately, maybe that would cause it?
Yes, incontinence is a definite possibility. And it may or may not be caused by a urinary tract infection. I recommend you have your dog checked out by your vet.
Marking territory is another possibility, especially if the visitors used the dog bed. However, generally, a dog won't deliberately eliminate in the same place he sleeps.
Have you seen him/her pee on it as if marking? Or have you found it wet with urine? Urinary incontinence could be to blame - sometimes it's a result of an infection or other medical concern, but it can also be situtuational or just a part of ageing. My friend's dog sometimes 'leaks' a bit - when I come over with my dog (her best friend) they wrestle hard and both tend to overdo it on the water consumption. After a while, she will leave little puddles where she's been laying (and is very embarrassed about it!).