Negative interest rates will primarily affect big players like for example pension funds, even at -0.75% percent interest these will loose a lot of money. And buying gold is not particularly easy / cost effective when you need to convert tens of billions of dollars. Not only will will you hugely inflate the price as you keep buying, but also introduce much bigger fluctuations than would result from deflation alone in the long term.

Lately, the Austrian central bank was rumoured to play with the idea of negative interest rates so the Austrian pension funds quickly brought up the idea of just storing their paper in secure vaults. As long as the costs of storage / protection are lower can the losses due to the negative interest rates, it's a net gain for the funds.

The central bank isn't directly allowed to prevent anyone from just getting their money in cash and while they could delay it by "process", only the government itself could issue a blockage on cash deposition.