So I want some kind of mechanic to represent that. Fortunately, Nightmares of Future Past has a system that suitable for adaptation. Each day, one of the PCs must make a DC34 Technology check. On a success, nothing happens. On success by 5+ (DC39 check!), the PC diverts HYDRA from the search, which is detailed below. On a failure, HYDRA advances one step towards finding the the PCs, and on a failure by 5+ (check result of 28 or less), HYDRA advances two steps toward finding the PCs. If HYDRA advances five steps toward finding the PCs, they find their current base and stage a raid the next day.
If the PCs make a direct attack against HYDRA, HYDRA enhances their search against the PCs. For the next 48 hours, a PC must make the Technology check every four hours to counter the more active patrols. HYDRA is at Red Alert for the first twenty four hours, and then at Yellow Alert for the next three days.
Modifiers on the check
+5 if HYDRA is searching rapidly (checks every four hours)
-2 if HYDRA is at Yellow Alert, or
-4 if HYDRA is at Red Alert
+2 if the PCs operate more than 100 miles from their home base, or
+4 if the PCs operate more than 1000 miles from their home base.
+2 if the PCs are laying low (not using their powers, communicating, or really doing anything)
Diverting HYDRAWhen the PCs successful divert HYDRA, the PC must make a new DC28 Technology check with all the same modifiers. On a success, the PCs add a Confusion step: HYDRA must remove all Confusion steps before they can advance on the PCs' base again. On a success by 5+, HYDRA gets a Confusion step and loses any progress they've made toward finding the PCs' base. On a failure, nothing happens, and a failure by 5+ (failing a DC22 check), the PCs have inadvertently tipped HYDRA off to another resistance group's base. HYDRA raids the other group's base and assumes they've eliminated the PCs, removing any progress the HYDRA has made to find the PCs' base.
At the PCs option, they may intervene in the raid against the other resistance group's base.