You didn't post which process You are using, so I'm not able to post any details.
In some PDKs are predefining guard rings as multipart paths, in others it is possible to make guard ring by placing appropriate contacts or by draw paths of nwell, p+ and "active" layer.
//edit: the contacts to well/substrate are not a cells from any library. Sometimes contacts to substrate exists in main process library but usually are used only on schematic.
You didn't post which process You are using, so I'm not able to post any details.
In some PDKs are predefining guard rings as multipart paths, in others it is possible to make guard ring by placing appropriate contacts or by draw paths of nwell, p+ and "active" layer.
//edit: the contacts to well/substrate are not a cells from any library. Sometimes contacts to substrate exists in main process library but usually are used only on schematic.