Every time we close a door, when we open it Skeeter is sitting right there...as patient as can be. Sometimes when he's in play-mode, he'll stretch his paws as far as they will go under the door--like he's trying to reach us on the other side. But, most of the time, he just sits there and waits. If he starts to get impatient, we'll hear his little "Brrrwow?", so we'll open up and he'll come in all ready for cuddles.
My kitty will wait at the top of the stairs and meow if i walk by, if he hears me coming up the stairs he'll sit on the other side of the door and meow as soon as it's opened, i don't know if that's guarding tho lol i don't think it is, but it's somewhat like your case. Oh yes and he also will sit outside the bathroom door but he will not come in even if the doors open, he must not like it :wink:
If I'm behind a shut door and my kitties aren't in the room with me then they are usually waiting for me to come out on the other side. Luckily, I don't do it unless I have to. The look mine give me is priceless. I'm sure they are thinking, "You're finally back!" :lol:
My kitties have learnt how to jump up and hit door handles so they never have to be locked out of a room... but on the odd occasion they do - like if i want to have a bath without a cat dipping his paws in so actually lock the door - they sit outside and meow and push their paws as far under the door as possible.
Bumper is a pure guard cat tho - if I am in a room alone and some one walks in without me speaking to them first (like i have to invite my family into a room) he hisses at them until i pat him and tell him its ok then he is the friendliest kitty ever!