I have an idea for modifying a HD with a CO2 charge to propel acid into the HD's interior, for people that need to may need to destroy a HD remotely. Some kind of USB trigger device, and from online anywhere in the world, you can connect remotely, type in a password and acid sprays all over the HD's platters, rendering them unrecoverable.
Fire is a cheap and easy way to make certain it's gone forever; just make certain the fire is hot enough. They can be disassembled with a $3.00 Torx screwdriver. If Law Enforcement really wants you, you won't have any warning. They don't call or write in advance.
Did a job for a US Customs LEO, and he said that they can seize your laptop when you cross into the US, if you refuse (or fail) to give them access to any password-protected data they might want to look at. They can send it off to a forensics expert for analysis. I think there is a market for selling custom products like this, for people that would rather see data destroyed then put into the hands of "someone else", whoever that might be. Governments, thieves, etc...