First off, get a new pediatrician! You should sit Will down and talk to him face to face. Tell him that what he is doing in dangerous and he might hurt himself. Tell him you don't want him to hurt himself; it will only make him cry and you sad. Then suggest another alternative to what he is doing. If he is climbing on stuff that you don't want him to climb on, get him something that you are okay with him climbing on.
Have a place in the house, like they show on Nanny 911, that is a dicipline area. Yes, we have a 'naughty step'. It really works. When our daughter acts up we put her there. Sometimes just the suggestion of putting her on the 'naughty step' straightens her up.
All kids love to climb on things. It's fun! Good luck!