I agree with Jane on the Bridgeport. That's what I have. I got Nikon a large and he's on the smaller side for male GSDs (he's 4 years old and 70-75lbs). He started wearing it when he was about 5 months. I may have punched another hole in the leather straps, but since it's an agitation harness it doesn't matter if it fits loose.
Liesje & the K9s
Nikon (GSD) U-CH SG Alta-Tollhaus Bono SchH1 KKL T1 FO PA TF-III FDCh-S CL1-R UJJ U-CA HIT TT CGC
Coke (All-American) VPC's Coca-Cola CGC, couch warmer extraordinaire
Indy (All-American) Blue Horizon's Indigo Girl, flyball star in training
Rainbow Bridge Kenya (GSD) U-CH Alta-Tollhaus-Krieger Lamb Chop CL1-R CL1-F RA HIT TDI TT CGC
vom Blauen Horizont / Blue Horizon GSDs