1. Use rope or thread instead: You can use rope or thread instead of swimming belt. As long as the rope or thread passes through the hole of swimming trunks, then it is tied tightly to ensure that the material of the rope or thread is firm and durable, so that it will not come loose when swimming.
2. Use a rubber band: wrap a rubber band with a suitable length around the waist of the swimming trunks, and tie the two ends crosswise to provide a certain fastening effect, but make sure that the rubber band is not too tight or too loose.