Oscar is a collieXhuntaway around 9/10 months old we've had him since the beginning of February. He is a big wuss, he and Penny get on brilliantly but other dogs seem to dislike him. Twice in the last week he has been pinned to the floor on his back, by a jack russell and a king charles cavalier spaniel (I mention the sort of dogs because they are considerably smaller than him) and he whimpers and looks terrified :( . The jack russell was pulled off and Penny chased away the king charles cavalier spaniel.
He is a very submissive dog but I don't really understand why these other dogs seem to home in on him and I'm not sure how I should react/behave.
Any advice would be really appreciated.