Some suggest lowering the FEL when stopped. Do you mean tilting the bucket so the front of bucket digs into the ground? I normally just drop the bucket fairly flat on the ground.
It depends how level your parking situation is. On level ground an empty bucket lowered and left in float position will provide a little drag. A full bucket provides a lot more drag. Lifting the front wheels with the bucket provides a lot of drag. I have a bigger machine, but I can dump (uncurl) my bucket until both the cutting edge and the top of the bucket can touch the ground. Some down pressure in this situation provides a lot of drag.
I try not to leave the tractor on a hill without being in the seat, just from lack of faith in the parking brake.
I also never leave the seat with the engine running. Made this decision a long time ago and do not regret it. Extra wear on the starter and battery, but much more safe. I had to buy a new battery a couple of months ago, only got 3+ years out of the original. $90 every few years is really cheap compared to a running tractor "running away".
Before you leave that seat with the machine on a hill think about which way you are going -- uphill so you can watch it roll away? Or are you walking downhill so it can run you over?
A wise old man cautioned me to always lower the bucket to the ground when leaving the tractor. Nothing to do with runaways. Kids love machines and will play on tractors. Imagine a pair of kids finding your tractor with the bucket up. One plays under it, while the other gets in the seat and pushes the joystick forward...