I think its great that your baby has another to play with now! As you know, any new dog takes lots of patience! Not to sound harsh, but I think its a little late to wonder if you did the right thing! Give it some time. Unfortunatley, I for one do not think getting that dog neutered will stop the marking. Been there with my Chopper and fixing him (after a year old) did not stop it at all. I've heard the earlier the better results.
Belly bands might have to be used forever in your house

And your baby may start marking his territory too. Boys....territorial!
I would walk two of mine, one in each hand. Works for me. Good luck with everything...
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God Bless our troops

R.I.P. Sweet Lexxi Girl - you were taken too soon, we love you always
Vixxen ,
Truffles ,
Gemma Lexxi and their mommy Trina- Girls Rule!