Don't most people expect to get some dirt under their fingernails when gardening, sort of goes with the territory doesn't it.
Can see a load of seed getting stuck under nails in soap.
TOP TIPRonseal
Yacht varnish would probably help keep my coloured finger and toe nail varnish from scratching and ruin when gardening.
Make sure normal nail varnish is thoroughly dry before applying and I suspect you would have to allow at least two hours for yacht varnish to dry after applying otherwise you'll get dirt stuck on, as well as under, your nails
By the way, it doesn't say anything on the Ronseal tin about this and it might just actually be impractical, quelle surprise
(posted with tongue in cheek and soap under toe nails

)