The simplest and probably most common way is brute force. Do not make a mistake in believing only big dominant dogs and use this method. If there is a point of weakness in your crate – any size dog can exploit it with some force. One of the most common ways dog’s brute their way to escape is by using their heads to force the bars apart. Cheaply made crates and flimsy metal are susceptible to this.
Most Helpful review (read the full Amazon review): “I have a 100 pound puppy, and travel crates are too small for him. This crate is very easy to set up and folds up very nicely into carrying case when it is not needed, saving a lot of space. I was able to fit it in my 2-Door car easily and take it with when traveling with my puppy on my last trip out of town. This is a very, very large crate and could easily accommodate…“
Addendum added January 28, 2013: My vet had never noticed these carriers because I had never put one up on the exam table until my last vet visit. She looked at it with interest and totally concurred with my opinion of having a small, but open carrier for my two (panicky) cats. She has seen more than a few overheated pets in too enclosed carriers. Since I live far from the vet I always carry spare towels for the bottoms of the carriers and she found that the "stable floor covering'* I use was an additional comfort feature for my pets long trip to their appointments. (I just ordered the larger size of this carrier for my "Phat Kat" and will donate her previous carrier to our local animal shelter.)