weedkillers

This weekend I need to do some serious weedkilling to some weeds on the path outside my house and in the garden. I intend to spray some weedkiller - however, am very aware that Brandy and Vicki both like to eat grass - I do feed them honest - I intend to keep them in from when I start to the following morning - however, I am naturally concerned about the contents of the fluid.. any ideas - I am growing the weeds I swear for a national competition and could win hands down.
Kev
Being sensible for once

I used this recipe last year, I found it on a garden board and got great results when I applied it to our weeds and our blackberry bushes-

1 cup salt
8 drops liquid detergent (I used DAWN)
1 gallon vinegar

Combine the salt and vinegar in a pan and heat to dissolve the salt. Cool the vinegar, add the detergent, and pour some of the liquid into a large spray bottle. Spray the vegetation. (You can also just pour the mixture onto the weeds.) Refill the spray bottle as necessary. Note that this formula will kill all the vegetation, so make sure that you are only spraying the plants you want to kill. If you need to use a lot of this spray, avoid spraying it near wells, as the salt can leach into your water supply.