Is there no one who can help me?

I know not too many blow up but it is annoying to fix and sometimes it blows up alot. I just want a way so the creepers are in water but the mobs still take fall damage. I jsut cant figure out how.

Can anyone help?

I was going to try to get some obsidian to do that but I don't know how much around I need to make obsidian and it will still blow up the half slabs

If you weren't on someone else's server I'd say, use the command
/gamerule mobGriefing false
It stops mobs from destroying blocks, and endermen from moving them.

Some servers have plugins that do this (or they used to, maybe some set this now?)

Try using obsidian near the spawner so they are explosion proof. You could also try stone half slabs, due to the game logic, if something blows up on its surface, it only destroys the slab (below it at least). Water or even just building with tougher blocks like cobblestone should help, too.

Can anyone help?