Now all possible deterrent means (ultrasound, fragrances etc.) have achieved no success, we got ourselves these herons Schreck. The instrument itself is quite well made (for the price but should be so) and at least for us tight. You can adjust the radius and width of the water jet. There is also a control for the sensitivity of the sensor. Everything works so far properly and without problems.
As long as there is no frost, the unit is from April to October with us in continuous use. And it really works, I've never seen cats run as fast. :-)
The only drawback: The unit does not cover the whole of our land, therefore can be found at the edge but still one or two piles. But at least you can calmed walk through the garden without having to brush your shoes behind.
From me full credit.