Female in Heat/Stray male

Question
HI, my husband rescued a female yellow lab a few months ago.  She is now in heat and a male black lab showed up at our country house a few days ago when it was below zero.  We found he let himself in on our heated back porch and didnt have the heart to kick him out with the cold temps.  We have placed ads in paper and on radio for found dog, but no reply.  He runs off for several hours ( like anywhere from 6-12) every day.  But always seems to show back up.  Is it possible he has a home not too far from here?  IF he does have a home, how long we he stick around here b4 staying home?  I live in a rural area farming community, no one seems to know who's dog this is.  I want to help him, but i already have 6 animals!

Answer
Count on having him as long as she is in heat.  Also count unbelievable attempts on both of them's part to get together.  It will get worse as she nears the end of her fertile time about the third week after the discharge started.  

He may have a home, perhaps miles down wind.  Once she is all finished, he may decide to move on.