Not sure if I should have posted this in "Sleep" but here goes.
DS1 3 1/2 has always been a bad sleeper. ie. Has never consistently slept through the night. We have essentially had the same routine with him since he was 5 months old - bath, story, tuck in, lights out - obviously modified as he has gotten older - brushing teeth etc.
He had always gone to bed pretty well and stayed put but waking multiple times a night.
However, ever since his baby brother was born 3 months ago he simply cannot stay put in his bed after we say Goodnight. He can be up and down the stairs for three or four hours. It's a nightmare. I kind of let him away with it at the beginning as I saw it as a symptom of the upheaval with having a newborn in the house.But now it is totally out of control.
The naughty spot simply doesn't work.
I have tried putting him back to bed silently but eventually he gets the better of me.I've tried reasoning with him and he promises he'll try to stay in bed but obviously the temptation is too much for him. 
For the past 5 nights my DH has been sitting in with him and silently putting him back to bed every time he gets out. He might get out of bed, oh, 50 times... Last night (the 5th night) was no better than any of the nights before. It took 3 hours before he finally fell asleep. To be honest I can't see this method working.
We just want him to stay in his bed. I know he'll still get up in the night but really need him to understand that "Goodnight" means Goodnight.
Please help. We are not getting a minutes break and are up all night every night between him and 3 month old DS2
TIA