Question
We have a 4-ft. stone walkway paralleling our front porch.  Any suggestions on
what to use to separate walkway from lawn and walkway from flower bed?

Answer
A trench edger that you  maintain with a weed whip or mechanical edger. Or any sort of edge restraint like metal edging, brick, stones, etc. If you have an aggressive grass then something like steel is better since it has not joints. You may also consider a plastic edger but I am not a big fan of its cheap look and often flimsy construction.

Good Luck