Take the feat Shape Soulmeld (planar ward)
The character must have a Constitution score of 13 to meet the feat's prerequisite, but that's all that's required for the feat Shape Soulmeld (Magic of Incarnum 40-41). Take that feat and pick the soulmeld planar ward, which says that it
protects you from mental control. It blocks any attempt to possess you (by a magic jar attack, for example) or exercise mental control over you, including enchantment (charm) effects and enchantment (compulsion) effects that grant the caster ongoing control over you. The protection does not prevent such effects from targeting you, but it suppresses the effect for the duration of the planar ward’s effect. (83)
According to Magic of Incarnum on Shaping Soulmelds (49-50), once such a character's had one night's rest ever, he can take 1 hour to meditate, shape the soulmeld planar ward, and for the remainder of the character's career gain the ward's benefits. However, an effect like the spell dispel magic et al. can for 1d4 rounds suppress the ward as if it were a magic item (52), and the ward's meldshaper level (equivalent to caster level) of half the character's level (that's zero at level 1) means that, while an area dispel will likely affect another high-level magical effect first, a targeted dispel will almost certainly render the ward briefly inoperative.
But unlike a potentially career-defining choice—like, for example, taking 5 levels in the prestige class church inquisitor (Complete Divine 26-8), taking 2 levels in the prestige class reaper's child (Dragon #299 47-8), taking the feat Insane Defiance (Elder Evils 13), or playing a needlefolk (Monster Manual II 158)—, the feat Shape Soulmeld (planar ward) is only a lone feat with minimal prerequisites and very few drawbacks, allowing plenty of room for character customization.
A note on magic items
While a magic item can provide the same effect, the price is usually prohibitive at the game's early levels (e.g. the eye of winking (Magic of Faerûn 158) (120,000 gp; 0 lbs.); the eyes of the spider (City of the Spider Queen 129) (212,000 gp; 0 lbs.); the phylactery of protection from evil (Dragon #342 68) (30,000 gp; 0.5 lbs.)). However, the banner of law (Heroes of Battle 133) (8,000 gp; 0 lbs.) is remarkable in its effect and reasonably priced.