You are concerned that your son is not completing his homework and also that he won't tell you when he has homework. You want him to be more motivated in school.
If he is not having any problems with his homework, give him some space. You do not have to monitor him so closely. He seems to be oppositional to being watched, and is rebelling in a passive-aggressive way. He will make mistakes, and will also learn from the experience.
Allow him to do his own work and then show you the final product. Try not to be critical. Give him positive feedback on his completed work. (He is getting attention for not doing his work. Positive reinforcement of negative behavior.)