Stand your pots on feet. This is good practice in any case as it helps to prevent ants from getting into the pot and nesting.

You can get little 'trolleys' for plants - these are plastic coated rigid wire with wheels on the bottom - the pots sit inside. You might not find any for small pots though, they're usually made for larger pots so you can push them around easily. Pound shops sell the smallest sizes, well, mine does anyway.

It's a lot more effort, but oil your decking with linseed oil.
Also, you could try moving the pots the width of the "footprint" on a daily basis......

you didn't say whether your decking is treated or in it's natural state. although decking is pressure treated to protect against decay, it will still absorb moisture and consequently suffer localised water marks. putting on a proper sealer is the only way to reduce this, as it will not stop a mark being formed by a permantly sited pot.