thanks for your reply and for cat rental offer! sadly my indifferent-to-voles terrier is less tolerant of felines (but then he is getting on a bit). no voles trapped last night for the first time in a week so perhaps i've made some impact on the local population? will try the cat litter trick as well.
Used cat litter may well work, or have you a small local zoo that you could get a bag of big cat manure from? I think I've also heard about putting gorse or holly down to stop them digging for bulbs. All else fails I can lend you my tabby cat, she's a mouser (and voler, and shrewer) extraordinaire, affectionately known as Little Miss Destruct-o-Kitty.
We back onto fields, and following this years harvest we have been inundated with voles. This the first year they've been a problem, and when out in the garden found they'd munched their way through half my (in flower) sedums, a patch of osteospermum, and looks like there are attempts at the salvias too.
What to do? No cats (might explain population explosion, last few years neighbours had cats, moved away), dog is indifferent but can't lay poison because of him, and im not a fan of this method anyway. I have covered traps down and currently getting up to 4 a night. Is there any other way? Would used (yuck) cat litter work? Any spray deterrent that won't harm the dog or my resident hedgehog family?