M.P.
I agree that he's testing boundaries but at the same time I know that his brain is not developed enough to know what to do about your no. He may know that he is to stop but his innate urge to explore is stronger than his ability to just stop what he's doing. So I recommend training. Instead of just saying no, redirect his activity. If he's playing with the TV controls, remove him from that area and give him something else to do. Once he learns that you want him to do something else you will be able to say go play with and name a toy or activity and you'll have a better chance of him stopping. Babies have short attention spans and do not have the ability to plan ahead. When he doesn't stop when you say no he is testing his world. "Does no really mean I must stop this. This is fun." He doesn't know what else he could do that would also be fun. And if you don't move him he isn't really sure that no means quit because you haven't followed thru and shown him what you want him to do.
He may eventually learn that no means move when you express frustration and perhaps even get angry with him. But he will have learned to move in order to avoid your harsh voice. He'll most likely move away and cry or even just stand there and cry because he doesn't know what to do next and because he is hurt knowing he has done something wrong by your standards but not understanding what he did wrong or how to correct it. He wants to please you. But his ability to understand the whole picture and make a decision on his own will not be available until his brain is more developed. Just as babies do not know how to crawl, walk, talk because their brain has not made that connection they are not able to reason until that part of the brain gets the connection. We are born with a basic brain that doesn't completely reach maturity until we're in our 20's. Parenting is therefore a process of training using skills that are appropriate for their child's age and ability to comprehend.
Self esteem is developed, in part, by teaching the baby and then the child ways to do things in a mannerthat leaves everyone feel good about themselves. When we get angry (and I'm not saying that you get angry but many parents do) we are telling the baby he is bad. We are punishing and not teaching. When we teach we are disciplining in a positive way. We want to teach our children to be proactive instead of reactive. "The TV is not a toy. You can play with your blocks." sort of exchange. When we just continue to say no a 10 month old knows he's to stop. But is at an age when he has only a little control that would inable him to overcome his basic need to explore and be independant. At first he doesn't know what to do next. By moving him you're removing the temptation and by starting him on another activity you are further diverting his attention as well as showing him something that is acceptable.
I'm not saying this is easy. Even the most skillful parents and caretakers aren't always able to be this proactive themselves. And teaching does take much more energy and thinking than saying no over and over. It is worth it because as he gets older he will be better able to make those transitions himself. He will know that when you say no you will follow thru and move him and that it is more fun to find his own acceptable activity than to wait until mommy gets involved. You have taught him how to be independent which is a primary goal for him.
I have found that saying stop is more effective than using no. The word no has negative connotations that are not aroused by the word stop. Stop tells the baby and the child and even the adult exactly what to do. It is a more direct way of communicating.