How do I bring heavy objects down a steep, unstable slope?

Flume.

Use a cable yarding system

If you have a tree at the top and one at the bottom run a rope and attach a trolley to the line, tie the logs to the trolley and lower with a rope. If it's heavy, loop rope once around the tree to slowly lower the trolley with the log. Once there at the bottom untie and get the next.

Kind of like a clothesline but with only one rope line. This way you have better control without a possible runaway. Unless of course you let go of the one holding the trolley back. Hence why you wrap it around the tree.

Depending on the budget the safest may be a cable system (the inverse of getting people at the top of a ski slope).

As a child I have constructed some 40' or higher hanging cable slides (It may be one of the reasons why I am getting a lower back fusion next month) the 20" x 18" log might be about the right weight.

For that you would need a solid tower or eucalyptus or similar tree.

The cheapest would be to use statistics.

first you have to calculate the probability of hitting the house if you aim a rolling log at the house.

if it is 5% you could roll 19 logs aiming at the house and roll no 20, 40, 60 . . . in a different direction.

Oops : statistics do not work that way.

The cable yarding idea sounds like a great solution. I can tie one end of a line from one tree/stump and attached the other to a tree where I plan to store the bucks. I just have to make sure I can pull the line tight enough.

I knew if I posed the question to some engineers they'd come up with some clever suggestions... except for the one based on probabilities. But that one made me laugh so it was worth it.