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I have an older unit (2nd gen it is WAAS system that was supposed to increase accuracy - not really anywhere from 5' - 50' ). I have used it on the ice but haven't marked any spots worth returning to LOL. Still put "bright eye" tacks on my tree stand tree/ turkey spots.
There is lots of good FREE information on the Pa Fish and Boat site. From the home page go to FISH / HABITAT / LAKE HABITAT IMPROVEMENT MAPS. This will take you to a county list. In your area there are maps for lakes in Butler, Beaver, Armstrong and Westmoreland counties and probably others. I looked at the map for Lake Arthur in Butler county and found that there is plenty of man made structure with GPS locations. I've used these maps in my area and found them to be very helpful. Some of the older location are not very accurate...apparently GPS's were not that great back then. I never go fishing, soft water or hard water, without my GPS.