When my DS started crawling he seemed to quickly picked up what 'No' meant and was at first quite easy about leaving whatever he was told to, or easily distracted at least...
He has just turned one and seems to have decided that the word is not worth listening to - he is forever pulling at cables, bashing at the TV screen and buttons, pulling things out of cupboards or (now that he has learned to open it) the freezer (brilliant!), bashing mirrors or our glass coffee table, playing with our shoes, crawling into the kitchen and rummaging in recycling box, trying to get bottles off the side of the bath... etc etc!
He has learned that radiators are hot thanks to his granny giving a sharp intake of breath and saying 'hot!' ever time he tries to touch. Now he goes up to any radiator hot or cold and copies her, putting his hand on it and breathing in o.@ -sigh-
We have baby proofed as much as possible. I try to just let him get on with the 'exploring' if it's not actively dangerous, until for instance i get sick of hearing half a word out of every show on Sky that half hour... But the things which are dangerous or when they become really irritating, a gentle 'No' or an explanation of why not (obviously he is too young to really understand but that is more for my own practice) has no effect!
He can be happily playing with his toys and the minute I move to do chores etc. he is up and into something he shouldn't be.. obviously most of the time I am playing with him or at least sitting near him and can stop him from getting into things before he gets there, but sometimes I have stuff to do!
I usually try three times to put him back with his toys but he just turns back around and goes for whatever he wants to do again! So after three I end up putting him in his highchair.
I don't want him to think of his highchair as a 'punishment place', he is already fussy with his food as it is - we don't have stairs as we live in a flat so there is no 'naughty step' and his attention span is too short anyway. I have tried a few light slaps to the wrist but either they are too light or he just really doesn't care and will carry on regardless - once got annoyed and the slap was rather harder than I meant and he cried and I felt awful - would really rather leave that for when he is older and should be able to be reasoned with!
Just don't know what to doooooooooo help please before he electrocutes himself :/ so far while writing this he has taken all hubbys payslips from file under my desk, screwed them up blah blah, pulled half a pack of wipes out of the packet, climbed all over his highchair fallen over and hit his head off it, and shredded several envelopes (I rescued the contents first..), tried to get into the kitchen 3 times but the door is shut (haha, until he can reach the handles!)