Is there a minimum size for the cover on an earth rod?

[ebee]

One obviously has to be able to see it in order to 'inspect' it but (as you go on to say), as far as electrical testing is concerned, I don't think there's anything that couldn't be done at the other end of the earthing conductor (i.e. at the 'MET').

he main one is to physically see and feel the joint is nice and tight and not corroded, if it were soldered/welded perhaps less of a problem, though

 

[JohnW2]

he main one is to physically see and feel the joint is nice and tight and not corroded, if it were soldered/welded perhaps less of a problem, though

Indeed. As I said, if one can't see it, one can't 'inspect it' (although one can 'test it')

I'm not sure that you's find many connections to earth rods which were not 'corroded'

 

[SimonH2]

Fairly easily (unless they are cemented down ) - but would the average electrician actually bother to lift them?

Would they even know it's there ?
All fine whike the OP still lives there and is compis mentis. But we're all familiar with "bought a house, found 'interesting' but undocumented things" situations.

 

[JohnW2]

Would they even know it's there ?

One presumes that if they were actually keen on inspecting the connection to the earth rod, they would follow the earthing cable and get a reasonable idea of where the rod might be.

However, I think that most of us would probably agree that 'under a paving slab' is far from a good/wise idea!