I have read wonderful advice on this board about behavioral training, from shaking a can of coins behind your back when they try to jump on you, to how to handle nipping. My question is, do you begin all of this immediately at 8 weeks, or are they too young? I know there is a period of time when they are young when they can have a negative experience and it can stay with them and become a bit of a phobia if you will, so do I let them get away with jumping up on me (won't be able to get very high and expect it will be oh, so adorable at 8 and 9 weeks!) and other antics when they are brand new to us, or do bad behaviors set in quickly?