>>>>"a plant at the plant that's a plant"
>>>
>>>Said Robert Plant.
>>>
>>>>How about: It's a good idea to get someone's ideas, blow the horn then dive to a great depth.
>>>>
>>>>You can use the same word 4 times there. What's the new sentence?
>>>
>>>Want to get me into endless loop trying to get to the bottom of this? I give up.
>>
>>In short: It's sound to sound, sound and then sound
>>
>>Dragan, you disappoint me!
>
>Sorry, I'm not really myself. I didn't know the fourth meaning of the word.

Aye, it just came to me when I was reading my book at lunch time, and I thought you'd get a kick out of it: "They ..., blew their horns and sounded". I thought that was a tautology at first till I realised that "dived" was what was meant.

ALso, to sound can mean to dive as well as determine the depth with a dunking device (How Mark Twain got his name)

>
>Say, if "undermine" means to dig under, what's the word to describe planting an explosive device under?

Ask a sapper. There may be a military expression for it but I'd say "undermine and mine"