Hi!
Ginger has some great ideas. If you don't have a coat, you may want to try the 'Belly bands' that are recommended for male dog incontinence, just put one around where the stitches are when your dog is outside. Most pet stores carry them.
Good luck!
I had the same problem last October when my dog was spayed, and we had rain. She loves to spend time outside, and even though recovering from the surgery (so she wasn't racing about chasing the frisbee!) -she had to go for short walks, had to go under a gate...etc.
I invented something which helped to protect her wound against dirt, wet. mud. I put a light dog coat on her which has a thin strap under the belly. Then I stitched onto the strap a wad of cotton wool which I covered with plastic film, so it was treble-thickness, and stitched carefully so that the smooth side would come into contact with her scar. Every time before she wore it I wiped it down with sterilizing alcohol, (waited for it to dry before putting it on her. And I wiped it again when we got back.
When we weren't out I took this off to make sure air would get to the wound properly. She did not wear this thing for long periods of time either. Only to protect her wound while she went out for 20 minutes or so.
Another thing is a cone collar of course which will stop her licking the wound when she is inside.
Otherwise it is best NOT to bathe the wound, but just to leave it open to the air and let nature take care of it. But do examine it a couple of times a day. If you see any swelling or redness, or if the wound seems to leak fluid or blood, take her immediately back to the vet to be checked.