phrasal
1. : extending over or for a considerable distance into an area
2. of military defense : extended for some distance forward from a primary combat zone and usually supported by successive lines of defenders and materiel
organize defense in depth — J.H.Plumb
3. : in marked thoroughness : covering a great number and often a maximum of elements, considerations, or relevant matters
here in depth is a portrait of Spain as it was and is — NY Times Book Review
making a study in depth of the effects of the broadcast — Gilbert Seldes