I think you need to be looking at a centrefire calibre, wounding animals doesn’t sit right with me and I always feel bad for it even if it is a fox or other vermin.
I went down the 22-250 route, possibly overkill but I haven’t had a runner yet and don’t expect to. My regular foxing land only really yields foxes to a maximum of 100yds but I picked up a new permission this Monday of 250 acres and having walked around it, I am looking at up to 200yds or even slightly longer, the 22-250 will then come into its own.
Unless i have misread it - im pretty sure the OP uses a .243
We all have runners - its a sad fact
I used a .270 for an age - and even had the odd one run - mainly just adrenaline - but it does happen
