perplexed by new signs of aggression...

[NandJ]

Hi. Our 2 1/2 year old corgi has started to snap at other dogs all of a sudden. Up until recently he was happy to be around and play with any dog any size any age. He always went right up and licked their lips and was ready to play Recently, during dog training class, he has begun to snap at other dogs when they get too close to him. This behavior seems to be leaking outside of that environment as well now. He'll snap at another dog who comes too close to him as he's chewing a rawhide. Or too close to his bed when he's resting. But, not always. Sometimes he's fine. Other times, not. 75% of the time he's fine with other dogs. But 25% he snaps (bites just in front of their noses...)and gives them the lip. Any ideas on why this might be happening and what we can do about it? It's disconcerting to see such a peaceful dog change behaviors quite suddently and for unknown reasons.

thanks for any thoughts...

N & J