You don't know much about Texas do you? Texas has a military past, the National Guard and reserves are very large (huge air assets, 15,000 army NG personnel, etc), the state supplied almost 16,000 active duty in 2004 alone (Canada had 28,000 enlistments from 2003 to 2008). They have had a Navy before, the Texas Rangers have often had to expand to battalion size military units when needed for major combat, the state has it's own Texas State Guard.
. Texas would be filled with fresh from active duty personnel to fill the slots need for border patrol and and military like slots.
Heck even the Confederate Air Force used to have it's own paratroopers until about the 80s, there is no shortage of highly trained and skilled people in Texas to replace the few Border Patrol that are there.
I don't see how you get "an angry mob" out of that.
How many Border patrol do you think are in Texas?
So you think when you secede that all you have to worry about are a few Mexican gangs. Do you really think that Texas has the weaponry and finances to take on several nations that are sworn enemies of the U.S. When you secede they will probably attack you. Who are you gonna get for allies and how do plan to resupply your newly formed military?