I would put both of them on a leash and let them sniff each other and I don't think it matters if it is inside or out.
If you have never owned a Great Dane you are in for a HUGE treat. They are the best, sweetest, loving dogs and you will fall in love.. The only draw back on owning one is they have a short life span...and they are lap dogs Ha!
I hope you have a great time with this rescue.
P.S. watch out for the tail....they can clean a coffee table in seconds. |