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Thanks IAP. My mum has insisted that I buy her that sonic pole thingummyjig, but I will definitely suggest the Jeyes Fluid method to her. I'm not surprised that moles don't like the smell of it, it's flippin' awful!
They may be nearly deaf and so not hear the sound made by that pole thingy, but the sound unit causes the pole to vibrate. In theory they should feel the vibration, which allegedly makes the mole/s uncomfortable enough to move on. Oh well, I've paid for the device now.
If we use a combination of that AND the Jeyes Fluid, that, hopefully, should have some effect. My mum's little garden is surrounded by a field that belongs to the house next door. It may encourage moley to migrate over there, but then again, I'm thinking that you're right IAP, more will probably just come along from the field to take it's/their place. Looks like this may well become an ongoing problem. Grrrr!