I am chuckling......first because I have a 140 lb. thunder chicken so I can see YOU throwing bits of liver in the hall and saying "Go get it boy!" and slamming the door shut. Despite the best attempts at re-training? His hearing due to seizures has gone very bad and the echo sounds now are enormously painful. The sounds he hears today are not like the great hearing he had when he was a pup. His ears are hyper sensitive and a simple motorcycle going by? Now causes him to be scared and behave irrationally.
Something I did learn recently I will share with you that is not pleasant. Boxers, boxer mixes and some bully breeds (this is us) but expecially Boxers are prone to brain tumors. Some times these start off as what appears to be hearing loss. This is where we were a year ago with Casper. Simple commands ingored, panting heavily, restlessness and finally siezures. The choices? MRI, surgery, chemo and at that; you prolong quantity of life not quality. The tell-tale signs are not coming when called, startling easier when they didn't used to at noises like thunder storms, motor cycles, loud crashes (because the sounds are altered in their heads), dopey head hanging, lethargic head hanging, uneven gait,(as if drunk) staring off as if (not kidding) stoned.
I'm not saying that Ace has this. Not at all. Boxers have unusually short life spans for dogs - average life is 7-9 years. A lot of people will say "Oh I have a boxer that lived to be 12 or whatever." I say Good for you. Average is 7-9 years.
The other thought I had which is decidedly less morbid is he's bored. You had said a few months back he was digging and had thought about putting in a sand box for him to really bull-doze in. If you did that? Good for you. IF not? Does he get at LEAST an hour a day of chasing a ball, or frisbee, swimming, running, bicycling? In addition to the digging? If not???? He's a very young 4 year old who is /could be (Auntie Star thinking out loud from a dogs perspective) depressed and just have a huge case of the BLAHS. Like - Oh BLAH - another day to ??? WHAT.....DO WHAT? THIS AGAIN? WHAT AGAIN? See what I mean? Tread mill could be helpful and it's easy to train him on it. It gets his heart rate up, exercise and activity for his muscles, endorphines,,,,,,,,and keeps him busy. If he's not listening it could be because he figures WHAT is the USE?
Another thing - and it's petty-----but when you tell him to get from the bed.......TELL HIM " ACE - OFF" and whisk your hand and arm in a sweeping motion with a snap........of your fingers......before you do this....and don't laugh....Make yourself as tall as you can, square your shoulders and THINK in your mind........I AM THE BOSS......and stare at him as if you were just FED UP...then snap that arm out, and in an authoritarian style voice - say "ACE OFF" not (DOWN) because down is lay down and well - if he's laying down? He's thinking - YEAHman......I'm a GOOD DOG....liikit here I am sssssssuch a smart guy.....I'm already down. HAHAHA....and he really may not get what ACE DOWN......expects from him. For all that matters - you could say any word......FARFEHNEUGHEN ACE - point, snap ....and point to the floor..
If he does NOT ....GET OFF the bed ......only say it ONCE........DO NOT keep repeating the command......(he's smarter than a 5th grader) Go get his choker and a leash......put that on his neck....and as you say ACE OFF.....snap the leash down towards the ground and with a pulling motion - pull him off the bed....and when he is on the ground....SAY .......GOOD ACE. OFF GOOD. Walk out of the room, give him a sit command ....then a reward biscuit. NO BISCUIT in the room. Maybe you would want to give the biscuit in his kennel? Or in his spot......You could even say------ACE SPOT......take him to in.....then ACE DOWN....when he lays down - hand him the biscuit. Or if you are opposed to treat rewards, scratch the small of his chest and say GOOD ACE, GOOD DOWN......or GOOD ACE GOOD SPOT. Or hand him a favorite toy....whatever your thing is....with him? That's his reward. We have a 3 gallon glass cookie jar and in order to get something from the cookie jar? Everyone has to be sitting - EVERYONE.......until all are sitting.....NO ONE gets a treat. 4 dogs in one tiny kitchen? You have to be creative. Especially when they are 140, 70, 55, and XX (pootie refuses to give her weight) lbs.
Everyone else probably covered this.....and you may want to just check the inside of his ears for mites or ticks. I think Steely covered that....other than sorry to be the bearer or the tumor news.....hope something here is helpful.