That area of Western Hidalgo County and Starr County border area are major smuggling routes. A lot of high speed chases and river splashdowns happen there too.
Not burning through a grant, in my opinion.
Edit: here's an idea of what happens in that swath of land you mentioned very frequently. If the get caught then they high-speed chase it back to the river and drive the vehicle into the water and retrieve the drugs in rafts.