One I've heard of for ornamental trees is Sucker Stopper. Don't know if labeled for edibles. Doesn't stop suckering but slows it waaay down.

Thanks! That's the stuff.

I see now that it's a natural plant hormone and OK on fruit trees.

The only slight downside seems to be a main use on trimmed or new suckers rather than preventing them on bare trunk but I can live with that and it will still be a big help.

In May/June, we were away for six weeks and returned to find such vigorous sucker growth on the trunks of our two lemon trees and one orange that the area above the graft was almost dead. In the case of the orange, all leaves had died!
We cut away the suckers and new growth has appeared. However I have to pinch out new sucker shoots every two days. This means that we cannot desert the trees for another holiday. We need to find a growth inhibitor available in Spain; the local garden shop doesn't know of one.
The trees are grown in pots on a penthouse terrace and we have an automatic irrigation system.