2 year old Border Collie German Shepard mix

2 year old border collie German Shepard mix, very sweet and loving. Found abandoned in rural Arkansas. He has allergies and was neutered a little late, displays a bad habit of marking. Crate trained, he just needs a lot of exercise, enrichment, and love and attention. Needs evaluation and treatment for his allergies. He is very attached to our female mastiff, separation anxiety from her, I would consider rehoming them together to reduce stress. They are both very sweet.