Wanted to put a Rocktopus in my pond so I modified one to be watertight and float nicely.

Tilted head down to keep center more in middle and plugged hole in bottom while increasing ballast so rocktopus will float and bob around and not go sinker.

Also making sure that big old empty head does not fill with stuff but progressively hollowed out said  interior so that mr rocktopus holds his head up properly.

If you plan to float it, I would not recommend PLA but rather PETG instead

If you want to attach rocktopus to a backpack, or a put a fishing line on, there is a curved out space on the back of the collar below the neck meat where you use as an attachment point. Note there are two versions of the model, first with just the space behind the collar and a second with a ring there already that you can print.

Note: there is a small hole in the very bottom of the base that allows you to poke the majick bean loose ... just use a paperclip, your phones sim card tool, or a thin drill bit to poke it into play.

The hole does not go all the way through but if you poke (or drill) through to loosen the bean it will no longer be water tight..so if you plan to put it in water you might want to plug that after the bean is loose (but you don't have to it will still float but may fill with water).

Maybe could be used as fishing bobber... the possibilities are endless.

Should print with infill set to 0 to maximize the internal hollow spaces... thusly you should also probably put the wall, top and bottom thickness to 2 or 3 layers (I do 3). That being said, no matter how you slice it (pun intended) the print will be porous so you should probably paint or coat it for long term floatability.

If, like me you plan to put these in a pond type setting with living creatures around then like I have done I would recommend if painting to use acrylic but more to the point you should probably use some sort of epoxy coating (the food safe type) on the outside. 

I used this:

https://www.amazon.ca/dp/B08VTQ1XVD?ref_=ppx_hzsearch_conn_dt_b_fed_asin_title_1

(got it for another project but it goes a very long way).