Benary's Giants were bred especially for the cut flower trade. Their plants have extra long main stems in order to produce a long-stemmed cut flower. Benary's Giants are nominally 48 inches tall, which is a foot taller than "regular" tall zinnias, which are 36 inches tall. Most, if not all, of that extra height is extra stem length.

If zinnias are crowded, they will grow taller in competition for the limited amount of sunlight. You say yours "grow huge", so about how tall is that? If zinnias are overcrowded, they can grow 6 feet or taller, but that isn't necessarily a good thing, because "stretching" zinnias can have thinner stems and branches. If a zinnia is completely uncrowded, it can develop strong side branches which can brace it against the wind.

Do you think that dogs may be running through your zinnias and knocking them down? Or is the damage mainly just from the wind? If it is handy for you to post a picture of the problem, we might have a better idea of what is going wrong. It may be that you need to give up the Benary's Giants and grow some 3-foot zinnias. But I have to admit that I plan to grow a bunch of Benary's Giants next year, with the idea of crossing them with some cactus flowered zinnias, as well as some zinnias with "exotic" flower forms.

Incidentally, have you heard about feeding your zinnias some soluble Silicon in order to make their plants stronger?

ZM