I always mic the tie knot like Nick stated, but I have moleskin layered over the hush lav my Cos-11 is encased in. I also make sure the mic element is poking completely outside of the hush lav. Works most of the time without fail.
LMC Sound use to carry a chest strap specifically for the Cos-11 that works well for hairy chests. Shipped in 3 sizes, but I'm not seeing it on their website just now.