I know how to get them there but I am having trouble getting them to stick. When they get there. I think the longest I have held a position is a month.
That depends a bit on the niche.
I got a niche where I achieved a top position over a year ago and I haven't been building any more links to it, but some very infrequent and occasional ones. It is one of the most stable sites I got.
I had other top of page 1 sites which gradually bounced back to page 2 without new links - in a matter of 2 months.
Depends also on the strength of the backlinks. Especially that low value links (profiles) seem to be good only for short term results.
Keep adding Backlinks unless you dont see dropping down. Reduce the backlinking rate when it continously stick to the top spot. Analyze your competitors often, thats important.