I find marker buoys helpful on big water. Usually in canoe country you can get a decent fix on a spot with the depth finder and by looking around at shoreline features a bit. If you are base camping and planning on really focusing on a particular piece of structure it might come in handy.

Remember, there will be a substantial weight with the buoy. If you are concerned about drifting off the reef after finding it I think a drift sock or an anchor would be better. Both will peg you fairly well to the spot.

I also tend to think the buoy might be better employed in the summer than spring. Fish tend to school a bit more tightly on mid lake reefs during summer and a marker could be helpful to mark "the spot on the spot". In spring they should be spread out a bit more and shallower thus negating the importance of pinpoint presentations (moving water excepted as they will congregate beneath it). Anyway, those are my thoughts......I hope they are helpful.