Here is a moldable glue with a family-safe formula that bonds to almost anything and can hold up to 2kg. The SUGRU glue is waterproof and easily cleanable. It gives you enough time to fix and improve your ideas but after 24 hours, the glue turns into a strong rubber that stays stuck.
You can mold this like play-dough into any shape and change it in 30–45 minutes. 8 pieces cost $22 at this time.