There are some planetary protection concerns about backward contamination of Earth by returning samples from Mars, a mission which may well happen around the Earth-Mars opposition of 2025. One of the concerns is that the return capsule could crash during atmospheric entry and landing and spread its content in the atmosphere/ocean/crater.
(How) Could a capsule containing a few kilograms or so samples from Mars be landed without any risk of leakage during the landing process?
A couple of wild suggestions to begin with:
The capsule could consist of an ablative heat shield or tungsten shell or something which would survive any atmospheric entry and hard landing scenario, given the return speed from Mars. The capsule would then be fished up or dug up intact. How heavy would such a capsule have to be?
Let the return capsule carry a nuclear bomb which can be detonated if the capsule is out of course. Even if in the atmosphere, it would only be about the 1,000th over-the-ground nuclear detonation made. But it of course assumes that the detonator does not fail, which is a challenging assumption in a scenario where something else already has failed. Probably not enough to calm those who worry about Mars bugs.