Take the guns away (even if you can keep them from such people), they'll use knives, table legs, a sock filled with change, whatever
When I was a kid, there was a man in our rural neighborhood that became depressed and suicidal. He tried to shoot himself. His family took away his guns and all the medications he could use to commit suicide. He went into a barn and hung himself with barbed wire.
A person determined to do evil or harm to someone else or themselves has so many options that they can't all be eliminated. At some point the individual should be held accountable for their own actions rather than placing blame on the tools they use.