It's worked for us to solve a regular problem, and has lasted through several days of very heavy rain.
Step 1: Ingredients
If you buy cayenne in fancy bottles, it can be pretty expensive, as much as $75 per pound , including shipping. But if you buy it from the bulk section of a grocery store, or in bulk packs with free shipping from Amazon, it can be less than 1/10 the price. Avoid getting too large a package, because its strength will decay with time after the package is opened. Two 1-lb. packages from Amazon for $14.24 seems like a great deal, if you are serious about this. Each pound is good for dozens of applications. Or you could opt for the organic variety .
For oil, you could use any vegetable oil you have handy. I used mustard oil , because I had a bottle of it around, and I thought it might help deter dogs. (I bought it for cooking, but haven't used for cooking after reading about occasional problems with it being mixed with Argemone mexicana oil , which is toxic, and because the bottles you can buy in the US are labeled for external use only, it's hard to be confident that it has been carefully prepared to food-grade standards. But I digress--any vegetable oil will work.
The wildflowers aren't needed for anything, but why not? Anything's better with wildflowers.