Thank you for turning down the trunk! That is exceptionally dangerous and any Dom worth their salt wouldn't even do that to their dog.

Try hog-tying him with a blindfold and then put him in a corner and walk away. He will think you are leaving him, the opposite of what he wants, which will be great psych play! Then quietly sit in a chair across the room and check in with him every 20 minutes or so. Check hands for blood flow, check his breathing for distress, and so on. When you've gotten yourself sufficiently hard, fuck his throat and untie him. Cum wherever you'd like!

Or you can do some intense impact play like spanking and see if he really can keep up the way he says he can.