Yes, you are right on! There are various ways to achieve the same affect. A frog or some weighted object with pins, is placed on the bottom, or floral foam with mesh or netting. I've seen marbles used.

You also need a degree of skill to be able to produce floral displays like the ones in the photos. Practice, practice and practice some more, if there is a floral art club in your area contact them. Wouldn't recommend the metal object with pins, it would be pretty difficult to disguise and tend to damage the stems of the blooms.

Agree completely with Mg. Once you have all the tools, it's about your skill, your vision, your creativity, your approach to achieve the desired affect. Look up "floral frog" on google to see all the different types and designs.

In a low container like those with a low symmetrical arrangement arrangement like those you don't normally need a weight. Wet oasis is quite heavey to start with.It helps to keep a few general principles in mind, eg largest flowers nearer the bottom, no oasis showing. No straight lines- -when working with several colours try to place them in a curve, possibly a diagonal one.

also select stems that are stiff naturally so they don't need wiring. keep the oasis damp to prolong the arrangement.