People have been building gates for thousands of years and the design that has won out is the diagonal from the hinge bottom to the top. This put the diagonal in compression which works better than having a diagonal in tension. You need joints which keep the diagonal in place and do not allow it to slip downward at the bottom. There's a number of ways of doing that - I, and others, can provide you with some joint examples if you need them.
Go into the world and do well. But more importantly, go into the world and do good.