My wheaten xs never have any problems with terriers out working but would never pen them with a terrier just incase but the 1st x bull wheaten pup ,he will be penned on his own from around 6mths old ,i have him in with the whippets at the moment so he will get used to being with other dogs because i will need him to work with dogs and not show them aggression ,and if he works out hopefully he will be my base for my next lurchers , with the grace of god i won't need for a few years yet