You can use corn gluten to block weeds. It's totally natural and non-toxic to plants and animals. It controls weeds by keeping them from germination (so it takes some time before this an effect), but if you are looking for a non-toxic solution to weeds, this is a good option. You can usually find it at local gardening centers.

Corn gluten also contains nitrogen, so if you apply it to your lawn, it acts as a fertilizer.