You have to intervene sooner. When you see a situation that might get iffy, intervene. Call him to you, diffuse the tension, change the subject if you will. So for example with the Spaniel was annoying him, call your dog away, shoo the spaniel away and give your own dog a break. If there are toys involved, watch closely, any signs of tension, call him away, diffuse, then try again. Though ideally I wouldn't allow play/interactions between dogs when there are resources involved. I do with my own dogs who live together, but not random dogs who don't regularly share space.