A few things that help
*High ac (95+).
*Spot and listen (you dont have to have super spot and listen some hiders have little hide and move silently because they know people wont bother putting points into it if they cant get 120+ in spot and listen, some cant even get high hide and MS).
*Wisdom governs the spot and listen skills ( if ya have extra room on ya items chuck on some wis to help out ya spot and listen).
*If the hider doesnet move dont move ya mouse around when they hide keep it in the same spot the hid in so when they come out of hide you can click on them straight away.
*Turn IE on before a duel to give you AC a boost and help try and foil there plans to catch you flatfooted.
*Attack straight away (start clicking on them before the go) so you can ether A. get them flatfooted or B. You dont get flatfooted.
*Horn.
*IKD.
*WoF.
*AoE spells (anything from lesser igams magic missle,ice storm, horrid ect and any dmg aoe spell).
*Greese/web/entangle ect helps if they move around alot.
*The Ampilfy spell (bard spell that gives +20 to listen).
*Sidesteping/run if fighting vs a melee hider so they dont get any sneak or there hide time runs out and there stealth cancels before they get you.
*Deflect arrows feat (also deflects other ammo).
*A decent HP (not needed but helps you for taking sneak hits).
*Dodge and Mobility feats.
*Uncanny Dodge.
*Empty body.
*Concelment feats.
*HIPS (when they hide you hide after them and get them when they come out .....dont go into hide first).
*Put some wall of blades up around you and in stragic places.
*Summons, animal companions and familars around you ....gives a higher chance of them misclicking and and good meat sheilds.
*DMG sheilds vs melee hiders.
*Death AoE magic (implosion,wail,werid.....maxed dc).
*Ask them before a duel if your really not up for the challenge if they wouldent mind capping there hides to X amount of times ( though alot of hiders know if they have a outright advantage over someone they wont go "pedel to the metal" on ya).
*Remember to have fun and not whine/be a sore looser or downright refuse a duel with them.