I made the dog toy below for our puppy Tess (see cutie pie picture). She's four months old and goes thorugh squeeky toys faster than I can afford to buy them. I went out and bought squeakers from the pet store (four for 1.99) and crocheted it. The squeeker is in the first section and in there in such a way it can't be migrated to the other sections. After a test ball I made had some issues, I made sure that these had no knots that could work their way out, and that all ends were long and hidden inside. By making them long, if she should happen to manage to get one out, it can easily be put back in. I also made it without seams of any kind.
For the pattern (fleshed out for here) I just started with a ch 3, formed it in to a circle, sc'd around it (about six times), and then kept going spiral like and increased/decreased to make the bubbles, changing color each time before I started in increase again. I found the best way to get a good shape is to increase a lot right at the beginning, do three rows without any increases, and then start decreasing. I made sure I didn't decrease too quickly to prevent holes. (holes are things teeth can get in to and make bigger) The last section I decreased down to about 6-8 sc left, and then cinched it up and burried the end inside using a tapestry needle. No stuffing since that seems to encourage trying to get it out.
I think you could infinately make it bigger, but some very large dogs could really destroy it. Tess is a whole. 6.5 pounds and will only make it to like 13. She's got sharp terrier teeth, but I think crochet is pretty indestructable.
I used some odd Sugar N' Cream, and size F hook. I went smaller to make it as dense as possible. This is number two. She's had the first one four a couple of days with not so much as a strand out of place. The weight/shape of it makes it easy to play fetch with, and since its cloth, I think it helps her teething.
She does colapse the separate sections, but by making it round, there are no real seams/edges for her to grab on to.