My dog tried to train me to give him a night time treat. When I let him out at night, I give him a treat when he comes back in after doing his business outside

My dog tried to train me to give him a night time treat. When I let him out at night, I give him a treat when he comes back in after doing his business outside. Then he got smart enough to scratch at the door to go out again, then came right back in and sat by the cabinet to wait for his treat. Finally he gave up on the extra treats when he found it didn't work. Dogs are very good at figuring out the actions they need to do to get a reward.