I wouldn't sweat this one too much but some easy fixes are:
(a) use a different looking mulch on the paths than on the flower beds; (b) log and rock borders like you mentioned; (c) use some string and stakes to rope off the flower beds so you know where they are; (d) line the flower beds instead of the paths with logs and rocks since the flower beds are probably smaller than the paths and will be easier to define.

Yup, I agree with Bob, use a different mulch.

Generally, I use shredded pallet mulch for the paths. And I use shredded leaves for the planting beds. Sometimes they overlap...

In some areas, like around corners I may add some raised edging just to keep stray feet away from the plants.