In this paper we deal with one of the art gallery problems, namely the problem of fault tolerant guarding of grids, which is defined as the problem of finding two disjoint guard sets in a grid. Although determining the existence of such a structure is easy in general grids, the task of minimising the number of guards taken over both teams is shown to be NP-hard even for subcubic grids. Moreover, we propose a 6/5-approximation algorithm for solving the fault tolerant guard problem in grids.