Then again, I found an amazingly nice ritually "killed" Susquehanna Broadpoint IN somebody's boot print once. Super fluffy floodplain soil had covered it when the guy stepped on it. Compressing it revealed it.
I wouldn't worry about the footprints in either creeks or fields. I would still look, I've found many in between rows of footprints, or after someone stepped on something. I'm sure those behind me probably found them in my footprints as well.