Is pest control even possible in an urban setting?

I am doing my best to follow permaculture principles in my little urban backyard. However, I don’t think pest control works. How to you create an ecosystem that allows a natural predator-pest balance when you are a little island in an urban jungle?

My main problem:

I’m fighting a losing battle with flea beetles on my brassicas. I would dearly love to grow arugula and turnips, or even radish, but they get eaten to lace before they are an inch high and die. There is no way that I can correct the inbalance of the entire neighbourhood on my own.