As a rule what I was told. Search once, then wait a week or more and try once more.
You should also read the log. If you find several of the previous visitors left notes that they couldn't find it, chances are it got muggled.
Also, I recently found one that was well away from its cords. Sometimes people move them.....dunno why.
As for the flooded one, that is just a no brainer. Wait it out.