Allocations should always be executed inside of the class initialization method. Specifically for the AVAudioPlayer class, initializing in the - (id)init method and calling -prepareToPlay fully primes the player.

DDViewController.m

#import "DDViewController.h"
#import <AVFoundation/AVFoundation.h>

@interface DDViewController ()
@property (nonatomic, assign) UIButton *sayButton;
@property (strong, nonatomic) AVAudioPlayer *audioPlayer;
@end

@implementation DDViewController
@synthesize sayButton;

- (void)dealloc
{
    if (self.audioPlayer.isPlaying)
        [self.audioPlayer stop];
    
    self.audioPlayer = nil;
}

- (id)init
{
    self = [super init];
    if (self)
    {
        sayButton = [UIButton buttonWithType:UIButtonTypeRoundedRect];
        sayButton.frame = CGRectMake(0, 0, 320, 320);
        sayButton.backgroundColor = [UIColor orangeColor];
        [sayButton setTitle:@"What the fox say?" forState:UIControlStateNormal
         ];
        [sayButton addTarget:self action:@selector(sayButtonPressed:event:) forControlEvents:UIControlEventTouchUpInside];
        [self.view addSubview:sayButton];
        
        NSURL *url = [NSURL fileURLWithPath:[[NSBundle mainBundle] pathForResource:@"fox" ofType:@"wav"]];
        NSData *data = [NSData dataWithContentsOfURL:url];
        NSError *error = nil;
        self.audioPlayer = [[AVAudioPlayer alloc] initWithData:data error:&error];
        [self.audioPlayer prepareToPlay]; // Preload buffers
    }
    
    return self;
}

- (void)sayButtonPressed:(id)sender event:(id)event
{
    [self.audioPlayer play];
}

@end