Look at what Col. Cooper does around his house; Couple hundred yards of white gravel covering the ground. Not exactly "covert", but, it will make someone heading towards your house stand out a little.
And in the "Old days", they used to have signs by the entry to a ranch etc., "Ranged for my 45-70" or whatever rifle they owned, basically reminding visitors to come in peace. As the places' owner knew exactly where their rifle would hit out to that range, maybe more.
In a SHTF situation I could see the people defending a given area marking an area as NO-MANS-LAND; it has been done before. Hoping that isn't any of our only plans for if things go bad, that helping others live will be in there somewhere, too.