For securing a network represented by a graph G = (V, E), one is interested in finding the optimal number of vertices where detection devices are to be installed. Suppose S is the subset of V with detection devices. Then a vertex in S is called a codeword and a vertex not in S is called a non-codeword. If every non-codeword u is adjacent to a codeword v where v is not adjacent to any other non-codeword, then S is called a multiple intruder locating dominating (MILD) set. The least cardinality of a MILD set of a graph is called its MILD number. For an infinite grid graph, however, we can only find locally optimal but infinitely replicable pattern, which in turn, gives the density of codewords in the grid. In this paper, we provide the density of optimal MILD set for infinite king, triangular, square, hexagonal and hexagon-triangle grids.

locating domination, infinite grids.