Can you clarify? I can only think of three kinds:
- people trying to hitch a ride on the unmanned launches to Mars - good luck lmao, they probably won't even make it past the launch alive
- another space agency taking advantage of the infrastructure without approval - could be an issue, but hardly an unsolvable one, with solutions ranging from sanctions to orbital and on-ground defenses
- somehow previously undiscovered Martian lifeforms, in which case we'd be too excited about life on Mars to be upset about infrastructure loss