Thanks ill look into itPersonally I just use a Fobus paddle holster when I OC. They're pretty inexpensive: got one for $15 used and the other $25 LNIB. They have a screw so you can adjust how tight or loose you want it (ie, make it harder or easier to draw). If I'm wearing a large enough t-shirt, it can still sometimes cover up, but I normally don't bother.
I don't think that the fobus paddles count as "retention" holsters, but IMHO, with the adjustable ease of draw screw, you can set it so it takes a good yank to get get it out of the holster.
(please, no edits on that last line, people!)