It doesn't have to be MEUs. I'd settle for a couple of Army Ranger battalions and maybe a couple of SEAL teams. Maybe with some armored cavalry tossed into the mix.
Well someone hasn't checked the force structure since 'Nam. There are only three Ranger Bn's. They all belong to the 75th Regiment, and are a Light Infantry force. Not exactly the force needed for securing a long border. There are more SEAL teams, but less personnel overall. They are also not equipped to be a Border Patrol. You know who is trained and equipped to be a border patrol? The Border Patrol. How about we enable those guys to do their job instead of pouring more military personnel into the situation?
as an aside:
Why are you guys so ready to get in a shooting war with the Mexican Army? I promise US soldiers have gotten lost and accidently invaded other countries, and for the most part we don't start wars over it. In all the real issues over immigration at our southern border a lost Mexican Army squad is pretty damn low on the list of "*expletive deleted*it to get concerned over."