Decades ago, I had RFI from various electric fences. The RFI was most severe on the BC band and 160 meters and much less so at higher frequencies. In all cases except one, this was from fences less than or much less than 1/4 mile away. The one exception was that there was a fence roughly 2 miles distant. I identified one or two of the bad ones, and the owners were happy to let me walk around fix their fence. It was most typically just a weed or branch touching the hot wire. At that time the units put out a pulse about once a second. It must have been a short duration steep pulse, since it was easily eliminated by my Ten Tec Omni noise blanker set at only a moderately low level which caused no detectable distortion. I have not bothered chasing down noise, since several rigs have easily handled it, and now there are no close neighbors who have horses. One clue is that the noise amplitude will be dependent upon the weather and the state of the weed growth, unless it is due to poor wire splices etc.
I have no idea how the pulses are generated in modern times, so some of this info may not apply. If modern fence chargers operate like the old ones, I would speculate that if an ordinary noise blanker does a good job of suppression, the fence is a strong possibility. Many other types of noise RFI are not handled well even in modern rigs with various noise reduction schemes. Rick KL7CW