You could get underwater cutting rods from BROCO
http://www.broco-rankin.com/broco/c_ultrathermiccuttingrods.cfm. We used them to cut up steal plates under water, requires oxygen to work properly. They will cut through everything so use with caution.
http://www.broco-rankin.com/broco/c_ultrathermiccuttingrods.cfm. We used them to cut up steal plates under water, requires oxygen to work properly. They will cut through everything so use with caution.