Buried urns, even if kept in a sealed sarcophagus, cannot be completely prevented from being eroded. A closed sarcophagus cannot be completely waterproof. With the naked eye, there is no hole. In fact, there is still a slight erosion, which will gradually seep. The urn inside is generally made of wood and jade, which is not completely waterproof. . . You can look at the iron blocks dug in the outdoor soil. After those things were buried in the soil for decades, not only did the skin rust, but the whole iron block was corroded by more than half. This is still a complete piece of iron, not to mention the box made of sarcophagus and wooden coffins. If you can make a coffin with a foot-thick iron plate and seal it with several layers of hundreds of pounds, it may last for decades or even hundreds of years, but how many people can do it except the ancient princes and ministers? So impossible! Ordinary sarcophagus and wooden coffins cannot protect the urn inside, most of the ashes have been degraded, and the rest will not be well preserved. What you take out is probably rotten ashes, which means little.
In addition, from the physical/chemical point of view, people are burned to ashes, which is a state change. If you keep the ashes, it is equivalent to cutting off the transformation, and it is equivalent to prohibiting him from returning to the natural cycle. I personally support the ecological burial advocated recently. For example, lawn burial and flower bed burial are finally absorbed by plants and return to the cycle of nature. There are many artistic shapes in it, which doesn't look like a place to put ashes. I thought it was a flower bed!
Of course, if your family's wish is to strongly demand the preservation of ashes, then converting to wall burial can save a lot of money, as long as a few thousand to 10 thousand. I suggest that when choosing wall burial, it is best to find the kind of column with only 2-5 ashes walls, each with a relatively large area. Some wall burial stations stand in dozens of rows, which are really ugly.