Help he won’t stay in bed

Our 21 month old son has been in his big bed about 4 months and we have had trouble on and off with him getting out of bed.
He has a very consistent bedtime ritual, bath, pj's, teeth, story, kisses then goodnight 7pm. But before we even get out the door he has jumped out of bed to come out of his room. We've been doing the super nanny back to bed thing, first time "it's bedtime Jarred", second time "bedtime", third time "bed", and the hundreds of times after that just quietly and calmly putting him back to bed. First day last week took 55 minutes, then 40 minutes, then 25 minutes but after that was all down hill 2 hours on Saturday night, we're at our wits end!
Last night after an hour we shut the door and after crying at the door for 10-15 minutes he went to bed himself, but woke at midnight and after 3 times popping him back to bed I shut the door again and he slept til 6:30am.
Naps are a joke, most days we have kindy or something for his older sister and he sleeps in the car fine, but at home in his bed is not his idea of fun. Shutting the door doesn't even work, he just finished crying for 30 minutes and fell asleep in bed only cos I stayed beside his bed and stroked his forehead.
He won't even stay still in bed for 5 seconds for the first half hour every night, please any suggestions greatly appreciated, we want some of the evenings to ourselves and to get some work done.

Edited by belmundy

Naps during the day might work easier for you if they are on a routine from day to day, instead of some days in the car and some days in bed.... as hard as that sounds with the other family things you need to juggle!

For the bed thing, when our girls were first put in a bed the door was closed every nap/sleep time. We are just starting to train Briona to sleep with the door ajar, so she can come out when she wakes up. But the freedom is pretty tempting for someone that age. So we put her to bed once, if she comes out without having her sleep, we put her back to bed and shut the door. The next night she gets the one try again, etc. Hope that helps, I do realise I'm talking about girls not boys but Briona does have a certain amount of "will"

Thanks for that feedback everyone, seems the shut the door when he gets up theory is working for now, he's getting the hint it isn't a game now, has been less than 30 minutes the last two days. Getting him to sleep at home instead of the car is hard when we live 15 minutes from town and preschool etc, he can't hold out and the car gets him every time, that's the breaks I guess!