Since many weed seeds are airborne no barrier short of roofing over your plot will stop them spreading. You just need to stop your weeds from flowering and seeding which is pretty straightforward. Just mow the lawn sufficiently often to prevent flowering.

Really? My worst enemies are creeping charlie, violets and crabgrass. Are those airborne?

Right, no, those particular ones are not airborne. My wording was 'many' weeds, not 'all' weeds. I was thinking of common lawn weeds like dandelion, thistle, groundsel, hawkweeds, etc.

A barrier could work for those creeping species as long as it was maintained and kept clear of runners. As would thorough cultivation of beds around the perimeter of your property.

Phew! :) Yeah, I'll have to keep those dandelions from going to seed, which will be a pain. I'm thinking of doing a flat brick or stone border, with one of those ugly black barriers beneath it. Will be easier for both of us to mow that way. Won't 100% block them, but will still likely help.

The edging will likely help, but you will also want to remain vigilant and remove any pieces straying towards your neighbors' yards at least every couple of weeks. I have a similar edging around my gardens, and both creeping Charlie and crabgrass can grow a foot or more in several weeks. I try to hand pull those types of heavily seeding or wandering plants within a couple of feet of the garden edge, though I just let them go elsewhere.

Also, to reduce reseeding and sprouting of annual weeds, consider spreading corn gluten about 3 weeks before your last frost since it helps inhibit seed germination. For dandelions, we remove with a spike type weeder, or you can just go out every couple of days and remove spent flowers so they can't go to seed, and bag and trash them since IME seed will continue to develop even after the flowers have been picked. It is quite difficult to remove dandelion seedheads without losing a few to the wind.