Marley is Scared of Aspen's.... huge tracts of belly??

While my house is being renovated, I'm staying with my parents. Their dog, Marley, is doing his very best to be respectful of all my cats' space. but I think it goes a little further with Aspen... Aspen fully has Marley under his thumb! Marley has lived with other cats before but they never wanted anything to do with him. this makes him sad - he's always wanted a cat to be his friend. hopefully Aspen and Willow will warm up to him! Don't you think he deserves it? what a good, respectful doggo!