Our Snoopy sometimes 'marks' a spot, for no reason. It got quite frequent whilst we were away with him and hasnt happened since we got back from vacation end of Jan. We have a female beagle as well so thought that might be the cause. Whenever we hear him get up in the night we let him out into the garden. During the day, if he starts to sniff about in the house we put him out. Oscar may feel the need to mark his territory, to stop him put him out the moment he starts sniffing around. He'll get the message.