safe terrace?

[Kiolcha]

hello
We live on the 6th floor with a very long tiled terrace. There is a gap about 15 cms high beneath the "railing" (actually steel and glass pannels) all along the outer edge of the terrace. We are getting our puppy next month and I am concerned he may try to crawl under the railing to chase pigeons and other birds who are frequent visitors? Does anybody know how big a gap can be considered puppy-proof?
Thank you
Kiolcha (new member)

[Dawnspell]

You just never know with puppies. Jasper as a puppy had a small metal type crate that everyone uses for puppies and are considered "safe". He managed to get his bottom jaw through a gap then got his teeth stuck and couldnt move I was there so no harm done but I then had to secure finer holed stiff plastic mesh to the outside so he couldnt do it again. Jasper is known for mischief and managing to get into trouble without even trying though