Do ultrasonic cat repellers upset dogs?

I want to keep neighbours' cats out of my garden because of fouling and annoyance to my dog. She's a toy dog, a Papillon. She barks frantically when she sees or hears cats, and she comes indoors stinking of cat pee because they spray my shrubs. Also I'm afraid that a semi-feral cat that visits might injure her. Thinking of buying a Defenders Mega-Sonic, but am concerned that a small (8 lbs) dog may be upset by the noise. Has anybody with a small dog used such a device please?