Make sure you are well connected with your bike (literally!). Worn cleats will make your pedals feel sloppy and could result in unintended release with terrible results.
Shimano SH51 cleats are a single-release which are slightly more difficult to release compared to the multi-release SM-SH56 cleat. Single release cleats are less prone to accidental releases on rough terrain.
To view Shimano's multi-release cleats, Click here.