we have a similar type bottom over here on the west side of Erie. Both my anchors are Fortress danforths and set pretty good. I usually pull them by slacking the line so i can pull myself almost right over them then tug straight up. Really about the only way, i do the short stern anchor first and i usually like a long lead on the bow so i'll pull myself out with the line and if i think its got a deep set i will let the boat carry some drift just past the anchor then pull up. Usually comes up with a mud/clay kinda stuff that needs to be splashed off.