i have an idea.
would he wear a little t -shirt vest harness ?
they make really tiny ones, i had one for oscar when he came home 12 wks, 4 lbs.
you have , for example , your phone #embroidered on it, and/or the words:
"check for microchip"
just in case he did get out some time.
http://www.baxterboo.com/dog/supplie...FcRM4AodrnE_Hg