I had tried about half dozen anchors on my 22 foot triple tube pontoon and none worked on the river even using two together didn't hold it, several years back bought a small sized box anchor and it holds my toon solid in the main channel of the river with a 20+mph north wind. Friends have gone through the same thing and saved some money and took dimensions of mine and made their own only rigid non folding and love it too.
http://slideanchor.com/store/index.php/the-box-anchor.html
i will b ordering 1 of these... i have 2 diggers for the 20' tritoon, but won't hold in 20 mph winds and waves with 50' out in 15 fow... tried running 2 - 1 on each corner, but with the bow swing only 1 holds at a time anyway... if you need more than 50' of anchor rope out around anyone pulling plugs or rigs, you're gonna have a mess...
wild - would you get another small or move up a size???