Everybody can fry a speaker just like pretty much anybody can blow up an engine. But like an engine, the individual has to want to damage the speaker. If you're listening at theater levels, you're not going blow these speakers. If you're trying to rock the backyard from the inside of the home and you have the speakers cranked to max Amp output and forgotten, sure, the potential to cause speaker damage is there. But again, the speakers would be damaged because someone choose to abuse them.
In your case, you'd need about 32-64w to push your speakers to >102dB @ ~4m. IIRC, THX reference is a room SPL of 85dB.
Are you planning on rocking the backyard from the inside of the house, putting the Amp on max output and leaving the volume control at max?