Would have to hire a lot of security personnell to keep the drug cartel away.
A lot of that goes into the set up. For example, the enclave should be in a (from the Mexican point of view) rural area. On the north side, an airstrip and access to transportation.
Gated access to and from, for authorized Mexicans from the south side of the enclave only; for authorized Americans to and from the north side only.
As such, you try and minimize and border crossing value to the cartels or for illegals. No illegal drug market in the enclave, or on either side; no easy access to or crossing of the border; no free access to medically uninvolved people.
About the only angle would be to try and hijack supply trucks going to the enclave. But even that would be easy to stop with a private highway.