The county where he worked for 30 years or so developed a retention problem over time, based on a couple of factors. First, they didn't keep up with surrounding counties on the retirement package they offered -- I don't remember the exact numbers, but it came down to how many years you had to put in before you could retire and get a pension, and the fact that our county was requiring a longer service than other counties in the area. Second, the schedule they required deputies to work was 6-2/6-3 -- 6 days on, 2 days off, 6 days on, 3 days off.
The end result was that the young guys who got hired on and who would ostensibly be replacing guys like my dad spent a couple years in our county getting experience and then got a job in a county with a better package and shift requirements. My dad, for a long time, was pulling extra half shifts and doubles because they were short-handed. The overtime was profitable I guess, but it was a real safety issue -- third shifts during the week, which is primarily what my dad worked, had all of 3 deputies for the entire county. If you got into trouble, backup could be as far off as 20 minutes, and if they were pulling a double they wouldn't be as sharp as you needed them to be when they showed up. This is exacerbated by the fact that, unlike the state police, deputies rode 1 to a car during the overnights, whereas the state cops always rode 2 to a car.
I think they've started to get the retention problem under control because the union negotiated a better package, but I remember it being a real issue throughout my childhood. The job really wore my old man out because they couldn't keep enough guys on to reliably cover the county.