Possible new addition !

O.K guys this has got to be the most posts that I have done in one day but Ive just got to tell you something.My husband is down at the lake where we have a trailer and boat and he just call and said that a dog has been watching him every where he gos....hes at the boat ramp and boat storage and that we almost had a new member of the family and me being the animal lover that I am and hate to see dogs killed just because no one wants them I said what do you mean ALMOST!!!He said he tried to put him in the truck to take back to the trailer but the dog jump out!!My husband will be home Sun. or sooner and I told him to keep looking for him and winning him over with food!Its a male,looks like a Border Collie with gray hair so thinking its an older dog.I know Im probablly jumping the gun but if he gets him and brings him home how do you introduce a knew older dog to a 60 some pound puppy??Any advice would be great! Id like to be prepared in case he brings him home! Thanks