Tack2000 is a great choice if you have the time. If you don't spray enough, the leaf and container, or allow to set up, you'll have problems getting it to stick. Works great if you've got the time or if the form you are covering has lots of curve/shape.
For quicker projects, hot glue applied to lower part of leaf and over lapping another leaf to hide the burnt part also works.
If you are covering oasis, a greening pin works great. Overlap leaves the same way, covering the pin.
After covering, foliage sealer adds a nice finished look but isn't necessary.
This was done with tack2000 and sealer.