OK, here is what I did.
1. Load Dog into scene. Do not change dog position during entire procedure.
2. It will be easier, if the default Dog 8 genitalia will be bigger. To increase their size You need to do few things:
- find "Female" morph in Dog
- right click on morph, go into Settings and turn off limits
- now when You will apply minus value to the Female morph (like -100%) the genitalia will be bigger - set the size You want
- now the balls are probably too big - make them smaller by use of Neutered morph
- now You have bigger base to connect D-9
3. Load K-9 into scene.
4. Move K-9 to the position You want it to be. Use only Z and Y Translate, and X Rotate. Do not use any other Translate/Rotate dials.
5. Once K-9 will be in the position You like, right click on K-9 in Scene Pane, and click on "Change parent".
6. Find Pelvis of the Dog 8 and select it. "Parent in place" checkbox should be checked.
It is done now. Try to move Your Dog, and You will see that K-9 is connected to it.
In my pic I used Oso3D Fur for Dog 8 to make the joint between Dog and K-9 look more natural. I think You can find is somewhere on the forum for download.
Try it, and tell me if it worked for You.