I like Supernanny's (Jo Frost) time out strategy and when DD is old enough will probably use that. Similar to BlackCat- a warning to stop the naughty behaviour they are doing or they will go into time out/naughty spot. if they do it again take them to the designated spot, get down to their level and look them in the eye. Explain they have been put on the naughty spot for doing xyz and will stay there for one minute per their age (so 2 years old = 2 minutes). if they get up from the spot, don't speak to them or make eye contact, just get them and put them back on the spot and the time starts again. Once the time is up go to them and explain again why they were put there, then ask them for an apology and hug/kiss.

Don't know if it would turn out to be that simple IRL but it seems to work for Jo! Lol