Duffy came in today and I talked to his owner a bit about the breed. She says that she hasn't heard of any higher rates of DA in the breed and of the three Glens she has met (in addition to Duffy) not one has been DA or DS. I've also not been able to find anything about them being historically used for dogfighting, though I guess it is possible. The historical information I have found says that they were used for hunting and herding.
My friend learned of the dog aggression issues after joining a breed discussion list and seeing a lot of people talk about having trouble with DA. Sometimes that is the best way to learn about a breed IME. A lot of GSD people are I don't know...in denial about the breed being prone to SSA but when you go to the GSD boards and there are always people asking about their two males or two females who've started fighting.
"The roots of the glen of imaal terrier lie in Ireland, and that is also why the breed has such a long and strange name that no-one besides glen owners and true dog enthusiasts can ever remember. The Glen of Imaal is a remote valley in the bleak region of Wicklow in Ireland, after which the breed has been named. There are differing tales of the glen's original uses. Most commonly the glen is said to have been used for hunting fox, badger and otter, as well as for various other tasks of the houselhold, such as controlling vermin, guarding the yard, turning spits and mills on dog wheels, pulling loads etc. Glens have also been used for blood sports such as badger baiting and dog fights for the sake of entertainment and the hope of winning a bit of cash for their masters in bets. Some (mainly working terrier owners) argue that glens have, in fact, never truly been used for hunting, but have primarily been companions with the other above mentioned uses. They claim that the hunting background is purely a misconception formed by the badger baiting and similar contests, which in fact have quite little to do with hunting and much more to do with the kinds of dramatic gladiator-like events that bull breeds were previously used for. " http://www.freewebs.com/seriousproblem/glenofimaalterrier.htm
"Some Glens can be dog aggressive. Some Glens are not able to live with other dogs. Most do well as long as they are socialized as a puppy and also have a firm guiding hand from the humans who live with them. Some folks have any number of Glens living together and doing well, and some have found that this was not possible due to hierarchy struggles. Glens can be very territorial with other animals.
In this breed, often the females are more assertive than the males in many ways. We caution about having two females living together as they sometimes will vie for the top-dog spot. It is usually the female in any Glen household that is the dominant canine-in-residence.
It is important to note that whether or not a Glen will become dog aggressive has something - but not everything - to do with early socialization and training. This trait can appear usually between ages 2 – 4 and generally is not amenable to change. It is either there…lurking in the genes - or not. Two Glens can be reared and trained similarly, and only one may develop this aggressive trait. It is a toss of the genetic dice.
It is also important to note that Glens do little posturing regarding their aggression. They can be deadly and act without warning. They are very strong dogs as well, and many owners have been pulled off their feet by their Glens.
Hierarchy is important to dogs but to Glens this seems paramount. They are exquisitely sensitive dogs in terms of hierarchy. It is helpful to become familiar with canine hierarchy and language when living with a Glen.
These are some realities about the breed best understood BEFORE you get a Glen."
http://glen-of-imaal-terrier.com/state1.htm