Well I think you need to examine your motivations -- do you not want her to have the dog because you're trying to punish her? I don't think any type of precedent is going to matter in a divorce proceeding regarding the dog, that's just something that would need to be negotiated along with everything else. Was it your dog prior to getting together, or did you get the dog together?

To your point rather than saying "I don't think that's a good idea" which invites a question, you could say "I'm not comfortable with that right now" which is more definitive and let it go at that. I would do a bit of soul-searching first however.

Acc

Married 18, Together 20, Now Divorced
M: 48, W: 50, D: 18, S: 16, D: 12
Bomb Dropped (EA, D): 7/13/11
Start Reconcile: 8/15/11
Bomb Dropped (EA, D): 5/1/2014 (Divorced)
In a New Relationship: 3/2015