Okay, so, this one might actually work. The way that urine-based repellents are designed to work is not by you — the home or property owner — peeing all over the place, but instead, using the urine or scent/essence of urine from other predatory animals. For the humble opossum, those predatory animals will include foxes, coyotes, wolves, and raccoons, although will extend to a few more beyond that, depending on the area. Essentially, the scent is designed to scare or bully the opossum away.
Usually available in liquid or granule form, you’ll probably pay somewhere in the region of $20-$30 for a 30-ounce tub of granules, and that might be enough to cover a relatively small patch of land fairly evenly. The bigger the area, the more granules you will need to buy, and the quicker your costs will rise. If you have a very large back yard that you need to protect, or need to use a lot of the granules to cover a number of spaces in your home, that $20-$30 will turn into $40-$60, and perhaps even more than that.
The effectiveness will decrease over time, of course, and this means that you’ll need to buy more and reapply, bumping up the price once again, and if it rains, any granules outside (or liquid formats) will need to be reapplied … The costs are mounting fast here.
If you have a relatively decent sized garden that needs three 30-ounce tubs to cover, you’ll be looking at spending $60-$90 each time, and it might need to be reapplied each month, or perhaps even more regularly than that. Even twice in six weeks will take the price to $120-$180 approximately, and you could have hired a professional to do the job for you, sealed all the holes, and gotten rid of the waste for that price … or close to it.