I've had this happen, but it's after I've gone too close and nicked a quick. I usually resort to clipping nails for a few trims and then gradually reintroduce the dremel. You may need to go back to the beginning and just do one nail at a time, give a treat, etc. When I started back, I could only do one foot a day.
I found it's much easier to sit on the floor and lay the dog on its back between your legs. You can scratch the tummy and get them relaxed first. I also trim between the pads that way. When I first teach them to have their nails done, I just put them in the position on the floor for a few days first with treats and scratching so they get used to it, then start nails gradually. Maybe that will help Casey get over his dremel issue.
The other thing to consider is that something is bothering him. Are his pads OK? Dry or cracked? Make sure nothing hurts. Try handling his paws when you're not doing nails to see how he reacts.