I don't know how things are in San Antonio, but I certainly would have no problems with picking on a park bench on the open green "park" areas of my South Carolina campus.
If you get questioned by anyone, tell them the flat truth - it's a hobby... and one of the more challenging and rewarding hobbies you've found (if that's true, of course ... it is for me). If you are telling the truth, you have nothing to worry about. As far as I know, it's not illegal to practice such things in public... you're a college kid also, which makes things easier on you.
If there's a homeless man on a park bench picking locks and he's seen by the city police, he will certainly draw very negative attention, regardless of his explanation. If a college kid is sitting on a park bench nonchalantly practicing lockpicking and he's questioned by a Campus PD Officers, he's got a much better situation. If it
is against campus policy or the law, you didn't know. You have a whole community of honest people online you can point the questioner to to back up your story... after all, it's the truth.
You may even catch the eye of a curious, outgoing individual who may look into the hobby himself/herself.
As I said, I don't know how things are there... but I would recommend not being paranoid and doing it wherever you want on campus.
*this is not legal advice. there's no guarantees that it's good advice either*
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