i've got a 4 year old staffordshire bull terrier that has always had a very small umbilical hernia, today i've noticed that it has got alot bigger and it is hard, just wondering if anyone has any ideas why it would all of a sudden got alot bigger
thanks

Take him to the vet as soon as you can. It could be that a loop of bowel has gone through the aperture and has become strangulated, (blood supply cut off); gangrene could develop.