If you take a milk jug of 2 liter bottle and make a cover for the end of your sprayer, it eliminates a lot of overspray issues.

just use distilled white vinegar, and watch the overspray!

I posted pictures of the deformed leaves here on gardenweb last year and nearly everyone who replied said it was round-up damage. It's weird though, because I spray when there is no wind, pointing away from the tomatoes. Could it be evaporating and after it is airbourne could it be settling on tomatoes?

About the vinegar--just the regular big jugs of distilled vinegar from the grocery store? Straight or diluted?

"Could it be evaporating and after it is airbourne could it be settling on tomatoes?"

Yes. What most people don't realize is that even if there is no wind at all (which almost never happens no matter where you are) and you spray directly onto the ground, there will still be a fine mist that lingers and that can be blown around or washed into the soil by rain.

Think of it this way: When you spray it, can you smell it?

If so, then small amounts of it are airborne and have travelled up to where your nose could detect it. If it can go that far immediately after spraying, it can go farther without much help.

Tomato plants are very sensitive to roundup and even a very small amount of it can cause problems - as you've seen. I'm also familiar with it from my neighbor spraying along my fence line near my garden. I spoke to him though and he won't be spraying again; I just have to break out the weedwacker every couple weeks and clear it down to dirt - worth it for me not having to lose plants like last year.

Could you use a mop to spread the Roundup on the the fence line instead of spraying it? Kinda like painting it on but no bending involved.

I put a ring of milled sphagnum moss around my garden which desiccates the weeds and forms a barrier they don't cross much and if they do I add a little more to bury them and they soon desiccate also. Milled sphagnum is cheap and beats poisoning our water supply. You have to put more down after a decent rain. I learned the effect totally by accident when I amended the soil last year and left a small pile of sphag. on the grass.

what about granular weed killer?

Get a brush and paint the weeds with your herbicide?

Thought I posted this... but alas I must have not after
the preview....

How about a shovel? Obviously not as easy as other suggestions, but it's guaranteed safe for your tomatoes and
something you won't have to repeat with a good layering of mulch.

Just another thought.....

It was asked "what about granular weed killer?"

Some volatilize when temps are above 50 to 60F - then drift on the breeze! Beyond that, granules are a hit & miss thing when you're trying to kill weeds.

Checkout the link below. Maybe you might find something your looking for. Ami

Here is a link that might be useful: Biocontrol Network