Our GSD, Bear is 17 months old and has been with us since he was 3 months old. He started exhibiting resource guarding behaviors towards our cats at about 7 months old mostly around thinking they will somehow steal his food. We do feed them at separate times and they don't hang around when he is eating. It has escalated to wanting to keep them away from us and anything he deems as 'his' by lunging and barking at them when they try to come into a room where he is with either myself, husband or both. We are constantly correcting his behavior by putting him in a down, trying to redirect his attention and verbal commands. He only does this when we are present and only in the house. He does not do this when we are out in the yard with him and the cats are out there too. We are watching for the 'before' signs such as ears forward, tense body and attention completely focused on the cats and attempting to stop it before he acts. He does well, and will even lay on the bed with them and then other times will go after them if given even half a second. We are now removing him from the room or whatever it is that he is currently 'guarding' as well as our verbal commands, downs and tie downs. He has also begun lunging and growling at dogs when he is on a walk. We immediately turn him away from the dog verbalize 'no' and if possible put him in a down. We use a prong collar while he is out on walks or in public and will use it for corrections. I think that whatever we are doing is obviously not working. We have worked with a trainer but cannot seem replicate most of these situations at training (he seems to know the difference!). We are wondering if an ecollar would maybe help stop this aggression. We are hoping to bring a cat friendly 15 month old female GSD in to our family soon and don't want to add oil to a fire.