yes
If they were rectangular they could fall down the manhole.
There are at least as many covers as there are finished manholes. Most manholes are already covered, and there are covers in stock ready to replace them, and covers in the factory ready to ship out. Unfinished manholes are relatively rare, but safety practices would probably require that random holes in a construction site should be covered by something. If you knew the proportion of unfinished manholes to stored and unused covers, you might be confident enough to boil it down to "There are at least as many covers as there are manholes."
The reason that manhole covers are round, and not square, is because a square cover could, when placed at the right angle, fall through the square hole in the ground. A circle, however, is the same diameter no matter where you measure it, and it cannot fir through a hole the same size and shape, no matter how hard anyone tried.
A circular manhole cover is used because it cannot fall into the hole it covers regardless of its rotation. This design simplifies installation and removal of the cover, reduces the risk of accidents, and is more cost-effective to manufacture.
If they were rectangular they could fall down the manhole.
You could use strong, sharp plastic tools on wood, but not on metal.
Many retailers sell plastic bed protective covers for children's beds. One could expect to find such covers at brick-and-mortar stores like Wal-Mart or Target. There is also an online shop called Bedwetting Store, which dedicates itself to child's bed wetting. One could find plastic sheets there, as well.
It depends how strong the chlorine is but I would dilute it first and then put it in. It could destroy the plastic and maybe even the toddler :/
The Plastic News is a newspaper that covers stories about processors, suppliers, companies, and end markets. One could visit their official website for more information regarding this newspaper.
It is called a "safety bollard" and can be purchased on line at numerous stores. Many companies manufacture them and there are different features and advantages to all. At Ideal Shield we have many different decorative covers along with our regular round plastic bollard cover.
I have two pieces of Murano luggage that are suede fabric with zebra stripe insets. They came with removeable plastic or vinyl zip on covers that could be put on for protection when the luggage was checked with the airlines. I want to buy a couple more of those covers.
Right Step Pro-Strength Super Polar In-Ground Pool Covers are pretty strong. Or you could build one from wood.