My DS is the same age as yours. He doesn't know what the word no actually means either. They're too young to understand boundaries & things like that.
I always say "No DS" & remove him from whatever it is he is playing with. More often than not he will just go straight back to the item so I just keep doing the same thing. So it is very repetitive but it's important to be consistent.
I also don't try to restrict him that much, in that I mean I don't have lots of out of bounds items. The only things my DS cannot play with are the power points, power cords, the oven & the cats bowls. So I have put away as much as I can, for instance I have put away the home theatre speakers as he was always trying to chew on them & it wasn't safe. I do think it's okay to let them explore as long as they are not in danger.
One thing my DS was always drawn to was our remotes on the coffee table. I have now given him his own with no batteries that he can chew & play with as much as he likes. It seems to stop him going for ours now that he has his own right there to play with. Maybe you could do something similar with your DS?