You can use something like this: http://www.amazon.com/Dahle-507K-Per...deckle+trimmer
I've been looking for something that will do larger prints. I've used a deckle edge ruler http://www.amazon.com/Westcott-Aluminum-Tearing-Mountai n-Deckle/dp/B00161SHAM/ref=sr_1_2?s=office-products&ie=UTF8&qid=1361497167&sr=1-2&keywords=deckle+edge+ruler
I use that wiyh a X-Acto knife, Kind of slow but gets the job done.