HuntingNet.com Forums - Stumped on the smallies

Guys I need some help. I must be doing someting wrong. I am fishing off the top of the dam in Mio Michigan. I learned from a guy fishing there that he has been having a lot of luck with a bobber+ split shot with leeches on a plain hook catching walleye and smallmouth. This guy had a 20"+ smallmouth on his stringer that day, so I believed him. I was having success using 8 lb test and had my line snapped a few times. I have gone to 12 Lb test because the crappy local store was out of 10lb. Anyway, I have barely had any luck since, I don't even catch the little walleye and rock bass I would normally catch. Is the heavier line too visable to the fish? I have tried crayfish tubes as well but the bottom is filled with logs and rocks, I get snagged every time. Any suggestions would be great.