A lot depends on how big/heavy this piece is. Also important is how smooth/rough is the floor you will slide it on. The main problem is the torque generated by the sliding. There are two types of casters (that i know of). One type uses four screws to attach a plate to the bottom of the leg. I do not think you have enough surface area to mount them to this kind of leg. The second option is a caster with a long pin at the top. You drill a hole and slip the pin in it. I think it may also be possible to insert a bushing into the hole and then put the caster pin in the bushing. But the issue you will face is the thinness of the leg means you wont have much wood to grip the pin or bushing. This could cause a failure (leg shatters) especially if the piece is heavy. It is possible you could laminate some additional thickness onto the leg on the inside, and attach a caster to the resulting thicker leg, but there would then be a risk that the laminated piece would sheer off. Maybe gluing and bolting on the lamination would be best. But in my opinion unless this is a lightweight piece, any of these ideas is risky. Congrats on your successful marriage. More on reddit.com

It doesn’t look too far weathered from the pic. Stains have poor results on teak wood. “Teak oil” is a name for a mix of linseed oil and tung oil that dries to a water resistant finish. There are also other drying oil brands like Waterlox and Daly’s that work well. No finish in the world will last on teak indefinitely outside. Some won’t even last a season. the advantage of drying oils vs varnish or poly finish is that you don’t have to sand to reapply if you catch it before it deteriorates. Sanding the chairs with all the slats will suck. I have used waterlox and Daly’s outside but not on teak furniture outside. By your user name I guess you live in FL, so your best bet is to cover it or store out of the sun when not using it. Source: grew up on a wood boat, spent many summers sanding and varnishing teak instead of with my friends. More on reddit.com

Ipe is probably your best bet. I find teak a bit soft for that kind of application. No finish. Let the weather do what it will. Above all, keep your expectations (or the client's) reasonable. There is no magic wood fertilized with unicorn shit that will look new forever under the sun and rain. Where I live, the air is very dry and the sun intense - even ipe won't last more than about 10 years before it looks worn out. Structurally it's as good as ever still, but it looks bad (cracks). More on reddit.com

Teak is a conflict lumber and is banned from import in the US and the EU. Sales of teak support the military junta in Myanmar. More on reddit.com