Having fun.       
You are just prepairing for a dive and then it hapens, your finsstraps break.

There is the next solution;

Perfectly adjust your fin straps each and every time with this exceptionally practical (and now quite affordable) pair of Springback Fin Straps. No need to readjust your favorite fins because your diving a different style boot that day. Quickest on, quickest off and highly durable. Wide rubber back with extended "grab tab" for additional comfort and convenience.

Designed to completely replace your fin straps and buckles. Fits all standard fins with standard 3/4 inch diameter swivel style fin knobs. Fin buckles feature quick release clips on both sides. Also available in an all metal Pro Model.

So surf the internet to find your local shop.