I've run into EMI problems near some sources, usually institutional lights (such as at some parks) and backyard
power lines in my typical city environment for hunting. (I've never had to deal with an electric fence, but I'm
assuming they cause similar problems, although maybe worse.)
In general with my original Red Racer, I've been able to greatly reduce or eliminate the audible interference
by using the frequency shift feature. Usually just moving up to frequency 4 from 3 has done the trick.
Sometimes I've had to try some of the other frequency numbers to maximize the noise reduction.
However, on a few occasions, the EMI is audible on all 5 frequencies. Then I've lowered the Gain, sometimes
as low as 40 or 30, and the noise has been reduced a lot. I can still hunt, although maybe I'm not getting as
much depth. And if any noise remains, it goes away after I'm about 10-15 yards/meters away from the EMI source.
Even with the Gain reduced, I've found that good targets generally come through loud and clear. Of course, I don't
know if I'm just not hearing some deeper targets. But low Gain still lets me hunt and find a lot of good targets.
It would be ideal if the Racer was never bothered by any kind of EMI, but I don't think any detector can guarantee that.