You can use a rubber snake,...simply put the snake on the floor & as the dog approaches (hopefully hesitantly) take the snake, slide it along the floor like a real one & make it lunge at the dog...........the doggy should get a scare & back off....if it does that's a good sign & should refuse to approach the rubber snake again. .....end of lesson, no need to continue.
If however the dog is more fiesty, place the snake on the floor again, & as the dog approaches, usually causiously, his entire concentration will be on the snake & when he's very near the snake give him a little pinch on a back leg,( do not hurt him it's just to give him a fright) he should jump in the air with fright.......he should now associate this & similar shaped objects with a fearful experience & not approach them...
You do realize that's almost the same method used to train dogs to hate any given species enough to deliberately hunt and kill it? You train coon dogs or squirrel dogs by letting a captured one bite them.