I have 4 girls...3 spayed...1 will be soon.
The only advice I can offer is to make sure that everyone is on neutral ground when the new dog is introduced. Keep them on neutral ground as long as possible, out at a park...long walk...having them all walking together...then when it is time to go home, everyone goes in the house together and nothing seems like an invasion by a newbie.
It worked 3 times for me. Mine have all bonded very nicely. Be sure your attention is not all focused on 1...
Since I have all girls, I am not sure whether a adding a boy or a girl makes the most sense.
Good Luck. I'll be watching for your upcoming news!
__________________  Lorene,  Paris, Paris, Samira, Aja  and the newest addition to our family... Halle  Belly Bands & Rag Quilts - http://2Parises.etsy.com  |