Aircraft interferance and Garmins?

[Foxhill]

I have been using my garmin with two 30 collars on my beagles for five months now and am more then satisfied with their overall performance. However I have had two experiences that have me wondering about their reliability in some situations. In both incidents my dogs were running hare in a club enclosure, with me following the action by frequently checking the garmin. Two weeks ago the collar I have assigned to "Nellie", suddenly showed her out of the pack, and then very quickly out of the enclosure heading east. My first thought was she was gone on a deer, but when the screen showed her hitting the shoreline and then proceeding several miles out to sea,I figured something was out of whack! (I live on an island off the northeast coast of Canada.) The dog screen showed her about 12 miles from my location out over the atlantic before I lost the signal. Since I could actually hear the dog during the entire time my garmin was telling me she was now running over the ocean, it was obvious the signal my unit was tracking was not coming from the dog. I experienced a similar incident back in May, but in a different location, and it was over 20 miles before I lost the signal.
I'm no expert on either GPS units or electronics, but the only explaination I can come up with is that somehow, some signal from an aircraft is over riding my system. The extreme distances I get the signal from suggests to me that whatever is transmitting it is obviously at a higher altitude then my pack of beagles! (This area is hilly and I'm lucky if I get a mile most days) This area is on a major flight path to Europe, so planes in the sky at most times of the day are common. Also, on the day of my last "incident", a major search was underway for a missing aircraft in this area so perhaps some specialized equipment that was being used in the search was responsible.( They eventually found the plane several miles off shore, under water.)
Anyone care to offer an explaination or theory? These incidents are really starting to have me doubt my garmin.

[wackysam16]

The same thing happened to us bear hunting one minute one of the dogs was on a mountain running then all of a sudden it was moving across roads we were on and headed to the small town like thing we got, and we followed it thinking somebody stole the dog then we came back and beeped him on the tracker and he was still on the same mountain only happened once and we couldn't figure out why, anyone knows i would like to know what happened too. We thought maybe a car drove by with a boat on a trailer and it picked that up but we don't know. And that all happened within 5 minutes he moved like that