This manuscript summarizes the process by which large trees are protected in Poland, how they gain protected status, and the use of acoustic tomography to assess the structural soundness of five individual trees. The authors discuss tree stressors and tree care options, and how the outcome of each assessment was used in the decision-making process. Moreover, the use of acoustic tomography as an assessment tool helps to gain public acceptance for the assessment. In sustainable development, there is talk of the conscious management of urban vegetation, and specifically tree populations in the city. In line with sustainable development, actions are taken to manage the existing natural resources, e.g., historic trees, properly. Thanks to using an acoustic tomograph, it is possible to diagnose old tree specimens, take care of the safety of people and property near the natural monument, and to test candidates for their eligibility as monuments. Thanks to the research presented, it was ordered that one poplar tree be left and observed in Lublin, that two linden trees be cut down in Sandomierz and Lublin, that arborist works consisting of lowering the height of a linden tree in Sandomierz be undertaken, and that monument protection be applied for an ash tree in Łęczna. A visual tree assessment (VTA) was the starting point for this research. Each of the trees could endanger the safety of site users, and the diagnostics performed using sound waves were crucial in assessing their health condition. Our results highlight that acoustic tomography is an essential diagnostic method applicable to trees belonging to cultural heritage, such as old trees, and is effective in preventive tree management through the monitoring of mid- to long-term changes in internal decay or cavities that are difficult to diagnose with the naked eye