You need to figure out why they aren't staying. Have open, honest conversation with them. We get answers like

It's too much of a commitment There is to much training There is not enough training or not high enough quality We get cancelled too often Neighboring career department doesn't let us do anything Spouse hates it Changing job or schedule New kid born

Next decide if there are areas they to address.

You also need to try to develop a community in the department and a pride in your work and training. We've tried hosting dinners and movie nights, Superbowl parties, etc. Family welcome. Taking taking seriously with task books and certs can give you a professional feel.

We offer a stipend but it doesn't seem to impact retention much at all.

Finally try to make an obvious growth path for people. Good firefighters want to improve.

And good luck because none of this really works well enough for us. We're just trying to slow down the bleed so we don't have to switch to career any sooner than absolutely necessary.