Ultrasonic Rodent Repellers

I was wondering if the ultrasonic rodent repellers are actually effective in repelling rodents and can be used in an industrial environment. Has anybody had any experience with them? Are there any limitations to their usage?
I have one side of the plant, I am working at, about 3,5 meters from an agricultural field which translates to permanent "attacks" from rats. There are many bait stations both on the perimeter's fence as well as on the external walls of the plant. Unfortunatelly the complexity of the plant's side is such that it is impossible to close all openings. Any suggestions anyone?

I have tried using ultrasonic rodent repellers and they did not have any impact what so ever. It is better to consult with a reputable pest control contrcator and work with them to control the issue at hand.


Cheers

Hello
As in Snitzels case our warehouse is also close to agriculture field, now that crop is harvested mice and rats come in. We have baits around and inside cardboard with glue everywhere but because our material is nuts and sunflower they are very attracted to goods. We also are now thinking about ultrasonic rodent repellers. Are there any more users that have experience with this machines?

I did a small search and found the attached file, that gives a brief history of the ultrasonic devices and their "effectiveness".

I experienced rodent repellers a wastage of money. We have to rely on strong integrated pest management program to cope with rodents