Well all I can say is that discipline is the key here !
It took a while for our 3 cats to lern not to disturbe me when I'm in my room (it is a cat free room, but not snake free Anyway it took about a month of screaming at them and chaseing to hit them back in the days but they learned that they are not allowed in there and now don't even attempt to enter even if the door is left open .So a little bit of tough lovin is the key