Constantly updating the website and continue banklinking it would help help to maintain the rank in google and would help you to rank higher.
Carry on doing whatever you did to get to that position in the first place or (if it wasn't link building you did) create quality, high power, relevant backlinks.
According to me those site content is more powerful and update regularly your content.Do off page optimization.Get more and more quality backlinks.
Continue building backlinks regularly and update your content. If you can hire some manual forum poster that would be very helpful.