How can I fix a problem my dog has with food aggression?

My dog is a big goof ball and thinks he is a lap dog even though he is 40LBS. He LOVES everyone and everything. He plays fine with other dogs, does not mind sharing toys or sleeping space. I bring him to the dog park often and he has never shown even the slightest hint of aggression towards another living thing. Lately though when I bring him to the dog park if another dog tries to drink his water (or I’m assuming food would be the same if he ate there) (he is the only dog in my house) he will growl and I’m afraid he might bite another dog if they really went face first into his bowl while he was drinking. This is recent and started about 6 months ago and I have had him for almost 2 years now.

What should I do to stop this before it gets worse or have I done something to promote this kind of behavior?

Also the only other time I have ever seen him get mad at another dog is if the dogs tries to hump him repeatedly and doesn’t get the hint to back off. Not sure if that plays any relevance to the rest of this but thought I’d mention it.