hi all - does anyone have any personal experience with these things. i was looking at something along the following lines: various pet fencing systems from petsmart i'm not very familiar with these things, so i don't really know if one system works better then another. in my specific situation, there is really only one fenceline (which backs up to an open ravine) that i need to worry about. the other three sides of my fence are all enclosed wood, but the one that backs up to the ravine is an open-iron design. i kind of like the wireless radio setup ... i think that way i can also train my pet to stay within bounds in the front yard. ---- it seems that they work by shocking the pet (obviously at safe levels) ... but does anyone know how effective that is? anyway, if anyone has any thoughts or opinions on these, please let me know. thx!