Help with my seven month old getting into everything!?

Now that my boy is crawling all over the place I have obviously had to baby proff my house. There are still things I have left out like my entertainment centre is on the ground and he can reach the VCR and some dvds. I have tried covering it up, but he knows it under neath. I have tried pulling him away and saying no in a firm voice but he just looks at me smiles and goes right back to it (or whatever else he is trying to get at) I have tried pulling him away and saying no in a firm voice and distracting him but that only works for one second then he right back at it. I'm at wits end trying to chase my little boy and replacing him in front of his toys just to have him go right back to where he shouldn't be. Any suggestions out there on what I could do?