Walking a dog in the heat

I live in southern CA and this is my first summer with my new dog, and with the weather getting warmer I am wondering about his paw pads and how to keep them safe when on walks. It gets awfully hot out here and I know that it can't be too good for his pads, but how do I know when it's too hot for him? And if it's too hot, are there any recommendations for doggy socks or shoes to keep him protected? If anyone has any experience or suggestions I would highly appreciate it. Thanks