How do you avoid being found again after a depth charge run?

[John Pancoast]

To add onto bstanko's comments, sometimes an escort will be pinging, but hasn't found you. There is a subtle sound difference, usually directional, between a search and a found ping.

Other comments pretty much cover the rest. The escorts aren't hard/much danger to get away from. In many patrols/campaigns I've only been sunk once by them (Nygm late '44). Rarely even get damaged.
I think one hit very close as I got heavy damage and a split second later another went off and sunk me.

Personally, I go as deep as I can. Well over 200 meters. Usually keep it at 2 knots to keep from sinking further.

If I recall, BOLD were historically released when a depth charge went off. I don't think it matters in the game. I tend to release them whenever I feel it's a good chance to confuse the escort. Release, go to full, change depth. I don't change direction; slows me down.
They work well, but remember once released, you've just confirmed to the escort(s) that there is a sub below. But at least for me, by the time I use one I've been found anyway.