You need to get at least 6' heavy chain for the anchor and make sure the anchor is the right size (15lb or so). 7:1 is the standard recommended ratio for scope (10:1 in heavy seas).
A quick search on Google also brought up this article, "The 3 Best Pontoon Boat Anchors for Any Conditions", by Pontoon Guide.com:
URL:
http://pontoonguide.com/3-best-ponto...rs-conditions/