We rescued a 3 yr old boxer Sunday. The fosters said they noticed he will grumble low if a dog approached while he ate. He is great with treats but I noticed on day 2 that when our puggle got near him while he ate his dinner that he did grumble at her. Any suggestions on how to correct this appropriately or should we just alway separate him while eating? He is a really sweet dog I don't want this to turn into a problem.