Searching Advice

[Erik_the_Viking]

Today we tried to find a wedding and an engagement ring for a poor lady that had lost hers. Unfortunately we didn't find them for her.

What I want to know is this: Is there anything we can do to improve our chances for her if we try again? The first thing to say is that she isn't even sure that she lost them on the land that we were able to detect, but, at this stage, I think she's willing to try anything.
The second thing is that the rings were lost in October. The ground where we were asked to detect was basically pasture ground. Now how deep could the rings have gone since October?
Considering that the ground has not had the grass mowed, or had any vehicles over it since then. I'd think they should be on or near the surface. With this in mind I didn't really want to excavate her garden like I was mining for gold! I was looking at the depth meter on the 'Nox (I don't know how reliable that is yet though). I didn't dig anything more than 3 blobs of depth.
The end result though was that we didn't find the poor lady's rings!
If I were to give it another go, is there anything I could do to improve our chances?

All that we did find was a load of agricultural/building trash (it's quite a contaminated area), and 2 decent buttons.
One button was a 4 hole button which had "Warranted Not to Cut" on the rim of the Concave side; the other was much larger, was brass or bronze, and had a sunray design on the front.