Poly glues like the one in your link are good but there is something to be said for soft set glues like silicone as well. They can help protect your leaves from breaking if bumped because they give a little. But poly glue can be painted, most silicones cannot.
Soft set epoxies are good, they give a strong weather proof bond but stay soft giving your work a bit of cushion. They dry clear as well. They are used on boats quite a bit.

Thank you very much, Pepper! Do you know of any brand names that I could look for? I live in a resort area and there are many marinas around -- should I head there?

I like G2 epoxy because it glues most anything. Check the link. Your marina will have something like it. There are smaller bottles as well.

Here is a link that might be useful: Epoxy

Evening,Snikkers.
I've used the LePage PL's ,but not on concrete;worked damn fine with styro.Another glue,a relatively recent arrival,is Gorilla Glue.This stuff seems to stick anything to anything else.I've glued eyes onto my masks and the suckers stick through rain,frost,anything Ma Nature has had in store.You have some working time(about 20 minutes or so)before the glue sets up.Watch for expansion-this stuff swells by 20%,so use only a little.I mean,a little.I have a small tube that seems to last forever!
Good luck on your bits and pieces.
cheers from here

Thanks, Rick!

I've seen Gorilla Glue in the hardware stores. Living in Central Ontario, I need something that can take great temperture swings. I'm heading to RONA now so I'll pick some up.

I used epoxy on this leaf and it worked out great, just had to sit still for about 6 minutes, till it hardened. I have also used the gorilla glue, it works great also, but it does swell a lot.
bonnie

If you click on the picture, you can see detail much better.
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If you are doing a green man, you can lay the face down in a pile of sand and add your leaves and crete, after it hardens you can turn over and peel the leaves off, then you won't need the glue.
bonnie

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Note to Gorilla Glue & any other urethane glue users...DO NOT GET IT ON YOUR SKIN!

Not toxic or anything, but...it turns your skin dingy black & nothing but time or sandpaper will correct the situation. It stays that way until the skin is replaced. Rubber gloves are a must.

Kinda' reminds me of an old "Cheers " episode where Miss Howe asks Woody if he understands the meaning of the word "insincere" and Woody replies..."Oh yes Mam, like "INflammable"...boy, I learned THAT one the hard way".

Cheers --- Tango