How breaching a wall can be sufficient to take possession. Plus, when one moves stones to benefit the land - that can also be a chazakah. Also, one who builds palaces on the property of a convert who died without heirs, and someone else comes along and puts the doors on the palaces, and thereby achieves the presumption of ownership. Plus, one who does any of the activities that a slave might do for a master - functions for the master to take possession, such as it is, of the slave.