Foot protection works are commonly installed in the outer banks of curved channels to protect the foundations of revetment structures from bed scouring. Since sliding failure of foot protection works can cause a disaster, it is important to establish a design method concerning the width of foot protection works which avoids slippage against local scouring. Yet, a conventional design method in which the width of foot protection works is decided by geometric conditions without take into account dynamic considerations has not been assessed. The purpose of this study is to clarify the mechanism of the deformation and sliding failure of foot protection works due to bed scouring while taking into account dynamic considerations. And, we develop a method of measuring the forces which make foot protection works slide down to calculate the width of foot protection works.