I've never had interference on mine. Once it pairs with your HRM, footpod, cadence sensor, whatever, it won't pair with anyone else's.

I REALLY value it for pacing, especially my first race at a given distance.

If yours has a vibrating alarm, it would be polite to turn the sound off. If not, I don't think it's a big problem. I hear other people's and it doesn't bother me.

If you have a footpod, calibrate it and set the watch to display pace from the footpod, since instantaneous pace is more accurate from the footpod than from GPS.