QuikCrete Over Pillows???

I'd like to start experimenting with using QuikCrete in my garden. I garbage-picked some small pillows (maybe 12" x 12") decorated with heavy yarn "lace" and 3D flowers. Does anyone have any idea how thick a coating of concrete I need to apply in order for the pillows to become weatherproof? (if too thick, I'll lose the detailing).

Any other thoughts how I could make these weatherproof besides many coats of poly?

Also, about how thick should QuikCrete be to hold up against the stupid maintenance guys' weed whackers?

In the same vein, I've seen "pillows" made of concrete with people sitting on them. Although I could make them solid, I then couldn't move them. Once I have experience using QC, I'd like to use cardboard or other garbage to take up interior space and then concrete an outside layer.

Would making something that a person could sit on (on the ground) require rebar or is just QC strong enough? How thick would the QC have to be to sit on it without it breaking?

Finally, if I sat on one of these pillows and it did break, would I get injured? I'm wondering if it broke, would just drop me 10" or so, OR would shatter into sharp shards?

Thanks for any thoughts, help, and feedback!