Not sure if soap is your best option. There are some good tips that people left, but here is what works for me. I am in the Rocky Mountains so deer are always a problem. Here's my method of attack:
1. If possible, plant Marigolds around the area where you want deer-free. These aromatic flowers are very unpleasent for deer and will keep them away!
2. Place an invisable barrier around your garden. A strong fishing line can be used as a fence around your protected area. As mentioned before, the deer will run into the wire and become spooked.
3. Urine. Deer hate the smell of human urine. Depending on the size of your garden or space you are protecting, you may have to collect a lot of urine. I've tried this before with good results. I saved a couple gallons of Urine and then spread it around the area I was protecting. The deer will mostly stay away, but there always is the one that is really hungry. This method works best when you are using the Fishing line method in conjunction.
Best of luck to you