I have a 4 yr old son who still has "problems" getting to sleep at nite. My olnly suggestion to you is this: Saftey 1st's Secure Grip Door Knob Cover. I use it on his door knob at nite and at nap time, to ensure not only my sleep, but his own. With giving him the freedom to open and close his door at will, he is testing you, I believe, on how far you will go to get him to stay in his own room. It wasn't easy at first, but eventually he got the idea, and learned that "sleep time" was for both him and Mommy, and that "Mommy needed to rest, too."
Good luck, M.!
And just so you know, I use it also for my 2 yr old daughters room. I started her out with it over 6 mos ago, and she is really good at staying in her bed and NEVER geting up, unless she needs to go potty, at which, i get up and take her. Using a "baby" monitor helps, as well, so you can monitor your child from any room in the house.
Take Care!