These "Possums" aren't playing "Possum."

The other day I went out to tend my compost maker. I have a 55 gallon plastic drum that I pile composting material in, add some water when I think about it, stir it once or twice a week (if I remember) and voila! Compost which is rich and grows stuff well. But I digress!
When I started to stir said compost, there laid an opossum on top of it. It was still alive!!! It didn't move much, but sorta hissed and bared its teeth at me. I thought about beating it to death since it was almost dead anyway, but that goes against my nature. So, I tipped the barrel over on its side and it came tumbling out and staggered away and thru my chain link fence to parts unknown. End of "possum sighting #1.
Day before yesterday, I was getting in my car, in the garage, and I smelled something dead. I went on my way, but when I got home, and pulled into the garage, the smell hit me again. So, I began to investigate. I found a dead possum in a trash can. Not the same possum either. This one was bigger. I dumped the trash can into another plastic bag, and disposed of the critter in the dumpster. BUT, the big question is, how did this varmint get into my steel walled garage, and then how did it get into a 40 gallon trash can? All I can think of is that it ran in there when the door was open for access while mowing the lawn. To get into the trash can, the rodent had to climb upon a bunch of precariously stacked boxes of Prof's stuff, then "dumpster dive" into the garbage can. Boy, I bet it was disappointed when it got in there and couldn't get out. This is a trash can I only use for "car trash" and contained only two cups from Starbucks, and an empty McDonald's bag. Not worth dying for, certainly.
But die it did. Stink it did. Where are these vermin coming from and how do I get rid of them? They have to be one of God's ugliest creatures. And I really don't want them around!!

Peace,
JE