I think until they reach a certain experience level you need to reward the marks every time and even then as much as you can.
So basically have a mooch where a mark is not likely not easy I know or as you say take a ferret but again not practical in the evenings.
With my terrier I used to ferret some right pain in the ass places on my own rather than drag him away until he got to the point where it was so ingrained I didn't have to worry much. But I suspect a lurcher will be much easier to go off the idea