I definitely agree with the post about big family walks and keeping a safety space - call it Leroy's room even - like a crate with an open end or a dog bed behind the coach, under an end table whatever might work best for him and your house set up. When Leroy's in his "room", instruct your boy that he must be left alone. This gives Leroy a safe space and then he can better control when he wants to interact and when he doesn't.
I also might add that sharing in a skill you start teaching at your son's age. Much like you start teaching them to ask to play with a toy that another kid is playing with, you can get him vocalizing and asking to say hi to Leroy. You could start doing this as well. As you approach Leroy, you could say, "Hi Leroy can I pet you? Or can I say hi?" Etc. Then decide what is the behavior Leroy does that signals he says yes. Maybe it's when he stands up or only if he approaches you.
And teach your son to start doing the same. Leroy probably sleeps harder than he used to and his startle response is getting mixed up with your son's presence. If you can get your son to give Leroy more time - from the asking the question and waiting for a specific response - that may help prevent the lashing out that Leroy is doing even when your son isn't interacting with him.