Anarchism is not simply the lack of rules / rulers. Anarchists believe in tearing down vertical power structures (hierarchies) and replacing them with horizontal egalitarian structures. We believe that society should structure along the lines of small unions of workers and neighbors and artists and whatever who gather freely to advocate for their own needs and desires and to coordinate efforts. These unions or communes if you’d prefer, would federate alongside other unions/communes to create a federation that works together to meet the needs of all. Should that federation stop meeting the needs of all or should new needs arise then the unions can defederate and federate with others.
This serves two purposes. 1.) It prevents these federations from becoming new governments (you can leave at any time) and 2.) It provides a system of organization that allows smaller groups to stand up to threats.
For a real life example that we are all familiar with. There exists this Anarchist “nation” called The Fediverse and recently a war lord by the name of Meta who attempted to infiltrate the federation of the Fediverse and the people recognized that this would upset the balance of our new egalitarian way of life. So all of the largest unions (servers) of the Fediverse organized and formed a new coalition to unite against Meta and prevent them from gaining control and shut them out of the process entirely. Thus they were able to protect the Fediverse and keep it going.
That’s how Anarchism will protect itself from outside influence.