Lifting stones to the chest….Hmmm. First, because you’ll be outside, if the mic is exposed, use a wind filter. Lavs “hear” wind unpleasantly. If there’s a lot to do with the chest, maybe wire the lav in front, behind the collar of the T-shirt, but run the cable up over one shoulder and down his back, maybe taping a time or two on the body to keep the cable from tugging.
You might be able to run down the front and tuck below one breast to the hip, following the body’s natural lines.
If you do mic at the collar, try to stay low enough so that you don’t get “under the chin” sound.
After this shoot, you’ll know a LOT more about what works and what doesn’t!!
Regards,
Ty Ford