What advice do you have for someone joining the border patrol right out of the military?

SGT(P) Daniel McBride Good luck in the Border Patrol. I had an uncle who did his full career on the Rio Grande and enjoyed the work - even the part about intercepting undoc'd crossers. They were for the most part very fatalistic, went back, and returned another day. His work went bad when he, alone, tried to arrest three US-based smugglers. They beat him badly and headed back across the river. Unfortunately for them, the Federales had observed their assault, and nothing more was ever heard from the three villains. Keep your eyes open and a buddy close to hand. Stay safe.

Study hard for your Spanish grades you'll really need the Spanish. Study your Immigration law like a mad man. Imma Law is tough and will serve you well after the Academy. Remember you will start as a Trainee, SGT (P) Daniel McBride. You may find yourself being directed ( there are no "Direct orders" in the Patrol), by someone younger than you (non military type) who will be your Senior or a Supervisor. Get ready for some office politics that will make your head spin. "Working Brush" is the greatest and gets you out of the office. LOL Strive to be your best in all the tactics you will learn at the Academy to protect your life. Remember, getting home at the end of every shift will be your biggest priority every day. I could write you a book. Message me and we can connect by phone if you'd like. There is a lot I can tell you. I was a Field Training Officer for 8 years and trained about 600 Trainees in those 8 years. Good luck my Brother.

Alberto (Albert) Castro Jr
Senior Border Patrol Agent (RET)

You will find that you have plenty of peers that have done exactly that themselves. Ex-military are very commonplace in the USBP. I'd suggest you seek out a mentor from among them.
Unlike a lot of mil to civ transitions, you'll find the Border Patrol to be much less of a culture shock.