Well, you know how to lose weight; keeping it off was always my biggest problem as well.
What about staying on FitDay and continuing to log your food and exercise, as well as staying accountable on the message boards even once you reach my goal weight? I'm thinking that will help prevent a relapse.
Thinking about it as more of a lifestyle change for your health rather than a "diet" that is over once you meet your goal is also helpful for me. Your eating and exercising have to be something you can sustain for a lifetime, not just till you lose the amount you want to.
A lot of the threads have goals set, or weekly weigh-ins, so joining up with those keeps you accountable and may give you the motivation you need.
Don't sabotage yourself mentally before you even start. You know you can do this successfully. And if you do slip up, like we all do, just pick up and keep going. Whenever I used to eat something I shouldn't have, I would immediately think I had blown it and took it as an excuse to eat everything else I wanted that day. That wasn't good. Then I found the quote in my signature and that gets me through that kind of thinking.