Marked one with a old toilet seat. One with a rototiller. One non valuable to anyone else marked with a nickle a partner sent to place where multiple holes had been dug, above a board buried above cache. Fail! wrong hole marked..board not found probing either, on my property..

Another site almost touches the north side of a support post.
One site had a bizarre elm tree I dug well under and reused multiple times. One current cache is off a distinct point, within a foot.
After one divorce, decades ago I was hasty checking sites,(time and access) and missed one. So a total of two have not been recovered.
No maps, but appears to not be a bad idea unless I misplace the map... l.o.l..
Here an out door dig not carefully insulated from freezing can be off limits for many months. Or a fire built above it to thaw, or a pick or spud to make a messy, hard labor attention getting recovery, or more risky when messy, addition to an existing cache or new dig started. Pre prepped in workable weather with a clever cover that blends in and can tolerate weight or by placing an obstacle above it, can work with care.
Many possibilities beyond digging but that's not your question...