Command help

So i'm making an adventure map, and there's a part where you're being chasen by a fox riding a redstone flying machine (don't ask why), and i need to make it so if you're too slow and the machine catches up, you die. This probably means i need a command that kills the player if it's on the same Z axis as the fox, but i couldn't find any tutorials for it and chatGPT had no idea about this sort of things.