In addition to the zero knowledge proof points discussed below, one could (if they had the mean) to not publish the tx but include it in a block that they work

In addition to the zero knowledge proof points discussed below, one could (if they had the mean) to not publish the tx but include it in a block that they work on privately. It's not fool proof (once you announce the block, you've only given yourself one block worth of proof of work lead and an attacker could copy your proof and include it in a competing chain) ZKCP is a much more robust solution.