I have Bruce for about 10 months now, and although he's an eejit I wouldn't be without him.
He's an inside and an outside door, basically if he wants in to sit on the sofa he's aloud to or if he wants to run about the garden he get's to. The only time he's in his cage (8' x 8') is at night when he's sleeping in his kennel, or when I go to work in the morning and no one else is awake (usually a maximum of 2 hours) and there's no problem getting him to go in there, in fact he leads the way.

My problem is though, in a months time the rest of the family are going on holiday which will mean Bruce will be in his cage when I'm at work (about 9 hours) and I was wondering if anyone knows how/ what I can do, to keep himself entertained?
He can chew on a bottle for hours while sitting in the garden watching the world go by, but I think he'd need more mental stimulation while in the cage for so long.

Anyone any ideas?

Can you get a dog walker to come take him out walking? Some people build digging pits or sand boxes for their dogs that gives them something to do. Biggest thing is make sure he has had a good long walk before he goes in so that he is really worn out. They sleep most of the time during the day. Make sure there are bones to chew on or give him a kong with stuff frozen inside when you first throw him in.

You will probably need to increase the amount of exercise your dog gets, especially before you leave. If it is 8'x8' I would think you could look into a ball on a rope and hang from up high. Like a tether ball? The frozen kong is a good idea. Also I am not sure what "puzzle" or mental stimulation games (brain teaser toys) they have out there that might be okay for unsupervised use but you might want to look into so thing like that. Is it large enough to have a little 4' kiddie pool for playing? You could look into doggie day care for one or two days a week just to spice things up. I like the dog walker idea too. Maybe look into some type of chew or toy that he only gets during that work kennel time to make it even more special. You could look into a food dispensing to and take some of his breakfast and dinner into the toy. You can make dog pupsicles of fruit or veggies in ice or water/juice ice.(peanut butter or broth too). Even just a plain frozen ice block is something different and fun.You can even hide toys/chews around the kennel for him to find.

I buy the tricky treat ball from Walmart with the treats. My dogs LOVE it, keeps them entertained for hours.