> What do folks use for marking a control point (in dirt, grass, woods), that might want to be maintained for a month or two ...
I've used the 60d nails a lot and they work fine - in the short term - but I'm wonder why nobody has suggested the old reliable wood hub and tack? If driven flush it can be mowed over.
In the cattle business it is simply referred to as "hardware". As they munch along on whatever interests them it is possible for them to ingest objects that do not degrade when exposed to stomach juices. Eventually the undigested object will move further along the digestive tract until it is physically unable to go any further. Then additional material begins to stack up behind this eventually resulting in a complete blockage. Some time prior to that the health of the animal will degrade and be readily apparent to humans. The cattleman recognizes the health issue as "hardware" and normally sends the animal to market to be sold for slaughter purposes only. The hardware will be discovered and retrieved in the slaughtering process. The other option is to perform surgery to remove the object(s). This is rare as such animals are not prone to cooperate in the long term with such delicate surgery, creating other health issues.
Common items might include bits of wire, broken or machine parts that end up in a bale of hay, indigestible plastic twine, almost anything small enough to get sucked up with a big mouthful of feed, grass or hay. Fence staples and nails would be fairly common.
It happened to us back in the '90s. Plastic hub tags attached to nails with hay wire. Two cows ended up dead with perforated digestive tracts. When the farmer opened them up he found the tags with our company name and phone number. The company had to pay for the cows and the rules were changed - only flagging and nails/rebar too large to be swallowed where livestock may be grazing.
Haven't seen any deaths from nails but if anyone of my guys pushes a pin flag in the ground they would be in big trouble. Those can be deadly.