How long is your rocker snowboard-

1. Sizing up. ---> longer effective edge which means less chance of sliding out.

2. Keeping the same size but buying a board with a different camber profile. Zero camber will have a longer effective edge than a reverse camber board of the same size because the contacts wont be lifted. Camber boards will have longer effective edge and also contact points biting into the snow a bit. 

3. Keeping the same size but buying a board with a reverse sidecut. If youre on arbor though you likely already have griptech. So probably not much help there unless youre going full on riding on rails like mtx. 

4. Just keep riding it in squirly terrain until you figure out how to just go with it :) 

People "warning you" not to go longer on a rocker board have a rather myopic view of what a snowboard is for. Short is great for throwing around and buttering on, but its not so great for float or stability. Reverse camber boards off-set the float issue, but they do it by worsening the boards grip and ability to deal with choppier terrain by bouncing you around a lot and throwing you off your line. This leads to instability obviously. For some people its fine because they dont tend to care that much about anything outside lapping the box/rail lines, mellow hits and just cruising the hill, but its not for everyone.  If its ot for you, then as i say, theres a few things you can do to change that. :)