Is this a good FBT setup?

[BettaShawn]

I am remodeling my fire belly toad tank and I need a kind of "consent" to begin construction. Here's what's going down:

Tank size: 10 gallon aquarium

1. GREAT STUFF insulating foam going 1/2 down the background and sides with the whole dried dirt over it.
2. Other 1/2 of the tank will be filled with water up/ close to the background
3. Repti-filter as filtration that I will try to hide in the foam background.
4. Plant it up with marginals

Here's my concerns:

1. Will the bottem of the background be able to be somewhat submerged in the pool of water?__will I just have to make that part silicone w/o the dried dirt? Because wouldn't the dirt become wet and therefore not stick to the silicone_or would that just be stuck on there since the silicone would be dried?