Now how do I put this....our lhasa apso bitch Tilly will not stop licking Bostons bits

....I'm not meaning the odd lick to clean him like she does his ears...it's all the time! Boston lies on his back with his paws in the air and falls asleep

We are really worried that she will make it sore or it will get infected, we keep telling her off and telling Boston not to be a ruddy doody boy but this is getting embarrasing when people pop to see us and we have a fllor show...it's just too much for my OH to watch

Has any one had this problem (with their dogs!!

) and why is she doing it? Boston sometimes gets fed up and growls at her to stop.