Moles in my own garden

Moles in my own garden - I woke up on Saturday morning to the sight of several molehills on our back lawn. My wife, having taken advice from our gardeners, bought three ultrasound devices, seen stuck into the molehills (above), which give off an annoying high-pitched beep every 30 seconds. The number of molehills has not increased overnight, so it seems effective as a deterent (I didn't want to lay poison traps for environmental reasons; there's lots of fruit growing in the borders. 

We've not had a mole outbreak like this before; our cat (which has killed several moles) must be getting lazy. Cut back on the Kit-e-Kat! To live, you must kill