How important is it to you to have a weed-free lawn? If you don't mind a few stray dandelions or a patch of clover here or there, you may not need to spray at all for weeds. If you have a typical suburban yard, you may be able to keep weeds to a tolerable level by pulling them out of the lawn and mulching planting beds to prevent weeds from growing around trees, shrubs, and perennials. A dousing with boiling water kills most weeds. (Use caution; the boiling water kills desirable grass and flowers too.) If you have persistent weeds and would like to use an herbicide, consider spot treatment with the nonselective herbicide glyphosate (Roundup). Glyphosate also kills grass and flowers and can damage trees and shrubs, so use it with caution. Glyphosate does not persist in the soil. Just be sure to keep your dogs out of the sprayed area until the foliage dries. As long as the dogs avoid exposure to the liquid itself, they're safe.