How to kill a big turtle?

[zxcvbob <bob at area51online_net>]

I just talked to my brother in East Texas.  He has a small pond with
tropical water lilies in it; some of them are unique (like a tropical with
red leaves), and a big turtle somehow found the pond and has taken up
residence.  He said it is a "pond slider" turtle, probably about 10 pounds,
and it has an appetite for his best lilies.  There are also some common
native waterlilies and lotuses, but the turtle leaves them alone.  He has
tried a turtle trap with a variety of baits but the turtle avoid the trap. 
He's only seen the turtle a few times, and never when he had a shotgun
handy.  The water is only about 3 or 4 feet deep, but it is murky and full
of weeds, so visibility is about zero.

Is ther anything he can put in there that is biodegradable and will kill
reptiles?  It is OK if it kills all the fish in the pond.  I don't think
rotenone will work because turtles don't have gills.

He has tried laying in wait for it with a pitchfork, but the turtle seems
to know it's being watched and it never surfaces where it can be seen.

I told him to hire a well driller or construction company to blast it with
a small charge of very high velocity explosive (like primer cord), but he's
afraid the FBI will think he's a terrorist or something and lock him up
with that shoe bomber :-)

Any ideas?  Thanks for your help.

Best regards,
Bob