Help with placing blocks

I made a block 2 blocks high and with an unusual shape.
I have a problem with placing it because the block levitates.
I would like the block to destroy itself when there is air under it.
I would like to remind you that the block is 2 blocks high and has an unusual shape, so you can stand on the block, but arrows pass through its upper part and you can place another block on it, which I also don't like.
Please help.