There is a verb "лаять", to bark and a noun "лай", a bark.
Собаки не кусают до/прежде лая. = Dogs don't bite before a bark. (лай in Genitive is лая)

But anyway, I don't like that phrase. I'd say something like: "Собаки сперва лают, потом кусают." or "Собаки не кусают до того, как облают."

What you have found is called "деепричастие", adverbial participle. It is not like English gerund, more like an adverb. It is more complicated to use but if you like...

Лая is (also) an adverbial participle of the imperfective verb лаять and can be translated as "during the process of barking". For your purpose you need perfective AP like "полаяв" (verb "полаять"), which is "after some barking".

So, "Собаки кусают только сначала полаяв" will do.

"Need to look first, then buy," - Покупать нужно, сначала посмотрев. "посмотрев" is an AP of "посмотреть"

APs in Russian are rarely used in speech, they are normally for the literary style.