Why can't we use fusion to make ourselves rich? As we know on fusing two hydrogen atoms we can convert it to helium and by breaking them we get two $\ce{H}$ atoms. So why can't we convert mercury to gold by removing 1 proton per atom?
While it is possible to synthesize gold from mercury-196 (exists as 0.15% of natural mercury) the resultant gold will be radioactive and will not be gold for long!

There is actually the spallation neutron source which creates gold from liquid mercury.

Wikipedia