STandard survey method is to set a permanent marker, usually a rebar rod driven below ground at each corner or point of direction change. The stakes with ribbons above ground are not ment to be permanent.
I wouldn't rely on short nails (even long ones). Too easy for them to be removed while doing land work, grading, etc.
Take pictures of the survey stakes trying to show their relation to permanent features to include in your records. Makes the permanent stakes a lot easier to locate in the future.
Sorta OT. Do the same the next time you dig up the septic tank if it doesn't have something sticking above ground. I have dug mine out every 5 years in the past 30 so I knew -exactly- where it was. Well last fall I cleared off the sod from it and found I was the tank width off of the location.
Harry K
Harry K