Koi

Ian says...

You can use rodent scarers which emit a high frequency noise that can deter rodents. These certainly shouldn't worry your Koi as high frequency noises do not penetrate water very easily and fish are more adapted to hearing low frequency waves, which travel much easier through water. However these devices may have limited affects on mammals, such as mink, otters and cats, some of the main predators. I would always suggest using two types of protection as some pests can become acclimatised to one form if left in the same place. The best thing, I've found, is to have two and interchange them every few weeks. For example, a motion-activated water spray would be an excellent additional deterrent to this.