srv, well, it depends.
"Retaining" a lawyer just means you hire one. Because of the flexibility of private contract that could be many things to many different people (check your state's Supreme Court's guidelines). As well, there are different types of lawyers, just like doctors or construction professionals.
When working for businesses, such as FFLs, I usually ask for several hours worth of work and then bill against that. Sometimes if I go way back with a guy, he just calls, sets up a time and we start in on it, no money needed to start.
In the world of the very bad things, where the tilecrawlers live, you will most likely encounter a flat fee. A very bad thing happens, and the entire flat fee is delivered to retain the criminal defense attorney. This will not usually include expenses for various things like expert witnesses, forensic testing or depositions.
In my world, it would be "unusual" for something to give me money for something that has not happened and they purportedly do not wish to happen.
Under my state Supreme Court guidelines, I would have to stick the money in the trust account and not touch it.
What you may want to do is just schedule an hour to talk to an attorney. Drop by your questions, and then go over them. I've done this before and think its very smart for all those who carry a pistol--where they can/cannot carry, definition of self-defense/lethal/non-lethal, explain the statutes, attitudes of potential jury pool, attitude of the Prosecuting Attorney, what to do after very bad things happen, etc., et al.
Just be aware that lawyers usually specialize, like docs. The guy who did your mother's will or does the taxes for Uncle Bill's plumbing supply company may or may not crawl on the tile and know the score in criminal court. Since the guys who come to see me are legal LTCHers (CCWers), they get sorted out in fairly short order and we spend a few minutes talking guns as well.