As far as the retention device on your holder, I would like to impart some words of wisdom that I heard a long time ago..."Murpy was an optimist."
As to the second part of your statement, I'm going to play devil's advocate here. Please understand this is only in the interest of discussion and not to flame anyone here.
We, as responsible firearms owners, are fighting a battle. It is a battle to protect our God given and Constitutionally given rights to bear arms. Our enemies in this battle are numerous, and range from the uneducated to the zealous anti's. We combat disinformation, emotional appeals, and downright lies with truth, logic, and facts.
We all know the catch phrases that are used, so I'm not going to dignify them by posting them here. My point is that appearances are very important, at least at this stage in our battle. We still have resposible, law abiding citizens having unfavorable encounters with law enforcement because of the "man with a gun" call placed by those who don't know better, or those who think they do.
My fear is that the apparel you describe (BDU's and pro-2A shirt) will be twisted into the terms "gun nut" or "military style swat gear" (similar to the way they use the term "assault weapon") by the anti zealot that calls the police. This could set our battle to educate the public back several years.
I hope that in the not too distant future, OC'ing will be recognized for what it should be...a person exercising their rights, not subject to government regulation or interference. The only way that is going to happen is to educate the public by exposing them to law abiding citizens OC'ing.
Make no mistake, appearance and attitude have tremendous bearing on how the public views you when OC'ing. If you're dressed respectably and act like it's no big deal for you to carry a gun, for the most part people will assume that it is okay for you to do so. If you're dressed inappropriately or are acting like you're breaking the law while carrying, the public will pick up on that and react. When I talk about inappropriate dress, I'm including any type of policital statements on your clothing. If you choose to wear that type of clothing, someone who may have ignored your OC'ing will decide that they don't like you and call the cops just because they don't like your viewpoint.
Is it right? Nope, but that's the way it is and the way it will continue to be until all of the following happens:
1) Everyone realizes that criminals cause crime, not firearms.
2) The 2nd Amendment is an individual right placed their by the Framers to ensure that the other rights are not screwed with
3) AND MOST IMPORTANTLY, people must realize that just because they don't like something, they DO NOT have the right, resposibility, or authority to tell other people how to live their lives.