If rocks aren't a major issue, I use a drain spade. They are hugely effective since you can cut a foot long 'plug'. The only downside is that they're a full sized implement but I'm already used to beach hunting with a scoop, so that's no big deal.
Took one on a relic hunt to a CW battlefield a couple years back, the other hunters all had the usual array of 'expected' belt-mounted digging tools. By the time we were done, damn near every one vowed they'd start using drain spades, too.
I use a hot tuned Fisher 1266X with a 12" Spider coil for relics and it goes deep. No chance I'm getting down there with a stupid Lesche and hogging out a hole when I can do the same job with a drain spade in 80% less time and 50% less bending over.