We've had a bit of an issue with Cooper and food lately. He was absolutely fine about food and treats etc when we first got him and was never possessive. Then when he was about 6 months we had to look after my brothers cavie for about 2 months while they were overseas. Now Rockford is an absolute pig when it comes to food. He's a cavie who will eat anything thats put in front of him and gulps it down in seconds. Our 2, Fergus and Cooper are much slower eaters. When Rocky was here he would try to steal Cooper and Fergus food all the time. Fergus didn't care but Cooper would get growly about it and occasionally bark and snap. We would say "no" and then try to train Rocky to finish his food and not go to the other bowls with positive reinforcement with treats which sometimes worked ok but sometimes they would just have to be separated.
Problem is since Rocky has gone Cooper remains very possessive about his food and can get growly at Fergus if he goes near his bowl. This has now been made worse by Cooper being confined in a pen following his knee op which seems to have made him feel even more vulnerable so if he has a bowl of food in his pen and one of the other dogs walks by the pen he starts to growl and if they stay too close he barks. He has even growled and snapped at us. We can see how the problem began and can understand why things are worse at the moment. We want to train this out of him especially before the baby comes but not sure the best way to train him, especially given that at the moment he's having the issues with his knees and trying to recover from that. Any thoughts / advice would be much appreciated.