recent personal experience:
we just added
a 3 yr intact mastiff male (pre-named Elvis) to our crew. Kado is about 5 yrs old & was neutered a few years ago. they are doing quite well.
i had all the concerns that i see expressed here. i did not get to meet E before he came today
about 6 hours ago. we have a very large yard so let E explore it, mark, & get a bit used to us. then we let out Holi but he was so exuberant in his wanting to meet her that he scared her. this did not surprise us since she is generally timid of dogs, esp. large one's since K ran her over. we put her back in the house & brought out Rosie. she is also timid around others & again, he was so exuberant that he scared her.
let me add some background on Elvis. the woman we got him from is in the military & married. she got E when he was a baby & she had a 2 yr daughter [now 5 yr]. she now also has 3 yr & 12 mth old daughters & they are trying for another child. she discovered that with working & caring for everyone, there was not much left to give E the attention he deserves. he got fed 5.5 cups at night then walked & then walked the next morning. beyond that, nothing much was done with him so i expected him to be quite excited when he got here. back to my experience today ...
we put Rosie back into the house, put a leash back on E's buckle collar, put a choker & leash on Kado, then did the scary act of introducing 2 adult male dogs. well ... everything went without a hitch! after a while we removed K's leash then eventually released E. by then E was pretty tired but they played lightly anyway. everyone is in the house now & E has been panting almost constantly; collars are still on the boys "just in case". we currently have E crated to try to get him calmed down.
   the worst part is all the humping! i know it is part of figuring out who's what but it does get obnoxious after a while. E keeps licking K's p***s and air-humping. K has growled at & snapped towards E to get some space. this has been going on for a while. when it was time for dinner, we gave E 2c food then ended up putting him back in the crate for digestion.
I am thrilled that things are going so well. i have introduced many dogs but my only experience with 2 males [both intact] resulted in a big fight. i would like to ask some questions. am I getting happy to soon? should i expect things to get more tense later? when will the humping stop??
thank you all for the advise. i'm hoping this will help julie & gweck with their current hopeful situation.